System and methods for improving fuel economy

ABSTRACT

Methods and systems are provided for controlling hybrid vehicle engine operation, where the vehicle engine comprises one or more cylinders dedicated to recirculating exhaust to an intake manifold. In one example, during an engine cold-start event or other event where temperature of one or more exhaust catalysts are below a temperature needed for catalytic activity, fuel injection to the dedicated exhaust gas recirculation cylinder(s) is maintained shut off, while its intake and exhaust valves are maintained activated, thus enabling the dedicated exhaust gas recirculation cylinder(s) to route air to the intake manifold of the engine, resulting in exhaust gas lean of stoichiometry that may serve to heat the catalyst. In this way, during cold start events and other events where temperature of one or more exhaust catalysts are below a temperature for catalytic activity, combustion stability issues may be avoided, and exhaust catalyst(s) rapidly heated, thereby reducing undesired tailpipe emissions.

FIELD

The present description relates generally to methods and systems forcontrolling a vehicle engine to improve fuel economy and avoidcombustion instability issues while maintaining low levels of undesiredemissions at low engine loads and during engine start events.

BACKGROUND/SUMMARY

Engines may be configured with exhaust gas recirculation (EGR) systemsto divert at least some exhaust gas from an engine exhaust manifold toan engine intake manifold. By providing a desired engine dilution, suchsystems reduce engine knock, throttling losses, in-cylinder heat losses,as well as nitrogen oxide (NOx) emissions. As a result, fuel economy isimproved, at part throttle loads and at higher load levels such asduring engine boost. As an example, by recirculating a portion of theengine's exhaust back to the engine cylinders, the oxygen in theincoming air stream is diluted and gases inert to combustion act asabsorbents of combustion heat to reduce peak in-cylinder temperatures.Because NOx forms primarily when a mixture of nitrogen and oxygen issubjected to high temperature, the lower combustion chamber temperaturescaused by EGR reduces the amount of NOx generated from combustion.Engines have also been configured with a sole cylinder (or cylindergroup) that is dedicated for providing external EGR to other enginecylinders. Therein, all of the exhaust from the dedicated cylinder groupis recirculated to an intake manifold. As such, this allows asubstantially fixed amount of EGR to be provided to engine cylinders atmost operating conditions. By adjusting the fueling of the dedicated EGR(DEGR) cylinder group (e.g., to run rich), the EGR composition can bevaried to include species such as Hydrogen and CO which improve the EGRtolerance of the engine, resulting in fuel economy benefits.

When one or more cylinders are dedicated to providing EGR, understandard fueling and controls, the EGR fraction in the charge flow issimply the ratio of the number of EGR cylinders to the total number ofcylinders. As an example, an engine comprising one DEGR cylinder out ofa total of four cylinders will operate at 25% EGR if all cylinders areoperated similarly. While such an arrangement simplifies engineoperation in terms of controls, hardware devices, etc., the simplifiedoperation results in a general lack of control over the system. Forexample, a key disadvantage is the inability to reduce EGR rate at lightloads, where combustion stability is a constraint. Another example wherelack of control may be disadvantageous is during transient conditionswhere the pressure of the charge flow in the intake manifold can changemore rapidly than the pressure of the exhaust in the exhaust manifold ofthe dedicated EGR cylinder(s), such as when the driver tips out of thepedal causing the throttle to close quickly. In such an example, the EGRfraction provided may increase significantly over the expected ordesired EGR fraction. Deviations from expected or desired EGR fractionsmay lead to undesired operating conditions, such as cylinder misfire,and combustion instability. As such, it is desirable to enable controlover dedicated EGR during light loads and transient conditions, withoutsubstantially increasing costs.

In another example, a disadvantage of operating an engine with one ormore DEGR cylinders is the inability to regulate the amount of EGRduring engine starting conditions. For example, during the early stagesof an engine cold start, the temperature of the intake passages and thecombustion chambers of the engine may inhibit the proper vaporization offuel. As a result, unburned fuel vapor may be delivered to an exhaustcatalyst of an emission control device. During such cold startconditions, the catalyst material in the emission control device may notbe at a sufficient temperature (e.g., light-off temperature) in order tosufficiently process the undesired, uncombusted by-products ofcombustion, and an increase in undesired tailpipe emissions may thusresult. In an engine configured with one or more DEGR cylinders, suchissues may be exacerbated if fuel injection is provided to the one ormore DEGR cylinders during a cold start event. For example, combustionstability may be further compromised, leading to the possibility ofdelayed engine start, engine stalls or hesitations, and excessiveundesired emissions.

One solution to reducing emissions during a cold start is the use of anElectrically Heated Catalyst (EHC). As such, the heated catalyst isbetter able to process undesired by-products of combustion. However, useof the EHC adds additional cost, complexity, and importantly, requires adelay prior to engine starting to allow the EHC to preheat the catalyst.Accordingly, improved systems and methods for engine cold startoperations, particularly in an engine comprising one or more DEGRcylinders, are desired.

U.S. Pat. No. 8,996,281 teaches a method of using dedicated EGR todecrease the light-off time required for a catalytic exhaustaftertreatment device. If the engine is determined to be in a cold startcondition, a valve is activated to direct dedicated EGR to a bypassline, the bypass line configured to route EGR gas to a point directlyupstream from the aftertreatment device, and directly downstream of anexhaust turbine. In such an example, the DEGR is optimized fortemperature rise, which includes operating the DEGR cylinder(s) at arich air-fuel ratio so that the EGR has high concentrations of H2(hydrogen) and CO (carbon monoxide). Furthermore, a secondary air valveis commanded open during cold start conditions, to provide O2 to thebypass line. As a result, the H2 in the DEGR oxidizes with O2 in theexhaust, and the H2-enriched DEGR is hot and not in contact with thelarge thermal sink of the exhaust turbine. As such, catalyst light-offtimes may be improved as compared to cold start events without DEGRheating. However, the inventors herein have recognized potential issueswith such a method. For example, costs and complexity of the enginesystem may be increased as a result of additional bypass line(s), bypassvalve(s), and air valve(s) to control O2 in the bypass line(s).

US Patent Application US 20160025021 similarly teaches flowing exhaustfrom a DEGR cylinder to each of an exhaust catalyst via a bypass passageand an engine intake via an EGR passage, and adjusting a relative flowthrough the passages via the bypass valve, the adjusting responsive tocatalyst temperature. As such, the bypass valve may comprise acontinuously variable bypass valve that allows a portion of the exhaustgas to be metered to an exhaust catalyst via the bypass passage, whilethe remaining portion of the exhaust gas may continue to be recirculatedto the engine intake via the EGR passage. In one example, US 20160025021teaches that during conditions when catalyst temperature is below athreshold, such as during a cold start condition or after an extendedoperation at light load, the bypass valve may be adjusted to increaseexhaust flow through the bypass passage while correspondingly decreasingexhaust flow through the EGR passage. In addition, the DEGR cylinder maybe enriched to provide a H2, CO, and hydrocarbon-rich exhaust stream atthe exhaust catalyst, where the degree of richness may be adjusted basedon the heat flux required to bring the exhaust catalyst to or above athreshold temperature. However, the inventors herein have additionallyrecognized potential issues with such a method, namely that the use of acontinuously variable valve, in addition to a bypass passage, mayincrease the costs and complexity of the engine system.

Thus, the inventors herein have developed systems and methods to atleast partially address the above issues. In one example, a method isprovided comprising, coupling an exhaust from one or more cylinders(DEGR cylinders) of a multiple cylinder combustion engine to an intakemanifold of the engine, and in a first condition, including a cold startand warm-up of the engine, shutting off fuel and spark to the DEGRcylinders while maintaining intake and exhaust valves activated on theDEGR cylinders (e.g. remaining cylinders), and resuming fueling andspark, and maintaining activated intake and exhaust valves on the DEGRcylinders in a second condition.

As one example, the first condition includes temperature of one or morecatalysts coupled to exhaust from the non-dedicated EGR cylinders beingbelow a predetermined threshold temperature needed for catalyticactivity, and the second condition includes an indication thattemperature of one or more catalysts coupled to exhaust from thenon-dedicated EGR cylinders has reached the predetermined thresholdtemperature. Furthermore, one example includes retarding ignition of theengine during starting of the engine under the first set of operatingconditions. In this way, by shutting off fuel and spark to the DEGRcylinders while maintaining activated the intake and exhaust valves onthe DEGR cylinders, air may be routed to the intake of the non-dedicatedEGR cylinders instead of exhaust resulting in exhaust gases lean ofstoichiometry. By retarding ignition to the non-dedicated EGR cylindersin addition to enleaning exhaust gases from the non-dedicated EGRcylinders, time needed to elevate temperature of the one or more exhaustcatalysts to the predetermined threshold temperature needed forcatalytic activity may be reduced. As such, combustion stability issuesduring engine cold starts may be avoided by stopping fueling and sparkto the DEGR cylinder, and by using the DEGR cylinder as an “air pump” torapidly heat the catalyst, undesired emissions may be avoided.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an engine system including a DEGRdonating cylinder group.

FIG. 2 shows a schematic depiction of a combustion chamber of the enginesystem of FIG. 1.

FIG. 3 shows a schematic depiction of a hybrid electric vehicle system.

FIG. 4 shows a flowchart for a high level example method for operating ahybrid vehicle engine where the engine comprises one or more DEGRcylinders.

FIG. 5 shows a flowchart for a high level example method for adjustinghybrid vehicle engine operation during an engine restart event, wherethe engine comprises one or more DEGR cylinders.

FIG. 6 shows a flowchart for a high level example method for operating ahybrid vehicle engine where the engine comprises one or more DEGRcylinders, responsive to a tip-out event.

FIG. 7 shows a flowchart for a high level example method for operating ahybrid vehicle engine comprising one or more DEGR cylinders responsiveto engine load below a threshold or a tip-out event, under conditionswhere engine operation is required.

FIG. 8 shows an example timeline for operating a hybrid vehicle enginecomprising one or more DEGR cylinders, according to the methods depictedin FIGS. 4-7.

DETAILED DESCRIPTION

This detailed description relates to systems and methods for operating ahybrid vehicle engine, where the engine comprises one or more DEGRcylinders. Specifically, the description relates to controlling engineoperation under conditions where engine operation with DEGR may resultin combustion stability issues, and/or increases in noise, vibration,and harshness (NVH) levels. The system and methods may be applied to avehicle engine comprising one or more non-DEGR cylinders, and one ormore DEGR cylinders, such as the engine system depicted in FIG. 1. Anexample illustration of one of the cylinders corresponding to thevehicle engine depicted in FIG. 1, is depicted in FIG. 2. The enginecomprising one or more DEGR cylinders may be configured within a hybridpropulsion system such as the hybrid propulsion system illustrated inFIG. 3. Responsive to conditions where engine operation with DEGR mayresult in combustion stability issues, if battery charge is above athreshold and engine operation is not required, fueling to the enginemay be disabled and the vehicle may be operated in battery mode wheremotor torque is utilized to propel the vehicle according to the methodillustrated in FIG. 4. Alternatively, the method illustrated in FIG. 4may be used to increase engine load above a threshold such thatcontinued operation of DEGR does not result in combustion stabilityissues, with the excess torque used to charge the vehicle systembattery, under conditions where battery charge is lower than a thresholdcharge level. If the vehicle engine is stopped, the vehicle engine maybe restarted, according to the method depicted in FIG. 5, and mayinclude differentially operating the vehicle engine and hybrid motordepending on whether it is indicated that the restart event comprises ahot start, or a cold start, event. Responsive to a sudden tip-out event,the engine may be rapidly shut down, and battery power may be utilizedto propel the vehicle, as illustrated by the method of FIG. 6, providedthat engine operation is not required. In an example condition wherecombustion stability issues may result with continued operation of theengine with DEGR, yet engine operation is required, fueling to the DEGRcylinder may be deactivated and the electric motor may be used for highfrequency cancellation of torque pulsations due to uneven firinginterval, according to the method depicted in FIG. 7. A timeline forcontrolling engine operation in a hybrid vehicle, where the enginecomprises one or more DEGR cylinders according to the methods depictedin FIGS. 4-7, is illustrated in FIG. 8.

FIG. 1 schematically shows aspects of an example engine system 100including an engine 10 with four cylinders (1-4). As elaborated herein,the four cylinders are arranged as a first cylinder group 17 consistingof non-dedicated EGR cylinders 1-3, cylinders that do not recirculate(route) exhaust gas to an intake manifold but only to an exhaustpassage, and a second cylinder group 18 consisting of dedicated EGRcylinder 4, that route exhaust directly from the second group to anintake manifold. A detailed description of each combustion chamber ofengine 10 is provided with reference to FIG. 2. Engine system 100 may becoupled in a vehicle, such as a passenger vehicle configured for roadtravel.

In the depicted embodiment, engine 10 is a boosted engine coupled to aturbocharger 13 including a compressor 74 driven by a turbine 76.Specifically, fresh air is introduced along intake passage 42 intoengine 10 via air cleaner 49 and flows to compressor 74. A flow rate ofambient air that enters the intake system through intake air passage 42can be controlled at least in part by adjusting intake throttle 20.Compressor 74 may be any suitable intake-air compressor, such as amotor-driven or driveshaft driven supercharger compressor. In enginesystem 10, however, the compressor is a turbocharger compressormechanically coupled to turbine 76 via a shaft 19, the turbine 76 drivenby expanding engine exhaust. In one embodiment, the compressor andturbine may be coupled within a twin scroll turbocharger. In anotherembodiment, the turbocharger may be a variable geometry turbocharger(VGT), where turbine geometry is actively varied as a function of enginespeed.

As shown in FIG. 1, compressor 74 is coupled, through charge-air cooler78 to intake throttle 20. Intake throttle 20 is coupled to engine intakemanifold 25. From the compressor, the compressed air charge flowsthrough the charge-air cooler and the throttle valve to the intakemanifold. The charge-air cooler may be an air-to-air or air-to-waterheat exchanger, for example. In the embodiment shown in FIG. 1, thepressure of the air charge within the intake manifold is sensed bymanifold air pressure (MAP) sensor 27. A compressor by-pass valve (notshown) may be coupled in series between the inlet and the outlet ofcompressor 74. The compressor by-pass valve may be a normally closedvalve configured to open under selected operating conditions to relieveexcess boost pressure. For example, the compressor by-pass valve may beopened during conditions of decreasing engine speed to avert compressorsurge.

Intake manifold 25 is coupled to a series of combustion chambers 30through a series of intake valves (see FIG. 2). The combustion chambersare further coupled to exhaust manifold 48 via a series of exhaustvalves (see FIG. 2). In the depicted embodiment, exhaust manifold 48includes a plurality of exhaust manifold sections to enable effluentfrom different combustion chambers to be directed to different locationsin the engine system. In particular, effluent from the first cylindergroup 17 (cylinders 1-3) is directed through turbine 76 of exhaustmanifold 48 before being processed by an exhaust catalyst of emissioncontrol device 170. Exhaust from the second cylinder group 18 (cylinder4), in comparison, is routed back to intake manifold 25 via passage 50,and exhaust catalyst 70. Alternatively, at least a portion of exhaustfrom the second cylinder group is directed to turbine 76 of exhaustmanifold 48 via valve 65 and passage 56. By adjusting valve 65, aproportion of exhaust directed from cylinder 4 to the exhaust manifoldrelative to the intake manifold may be varied. In some examples, valve65 and passage 56 may be omitted. In one example, valve 65 may be athree-way valve. In one example, valve 65 may be adjusted to allow allof the exhaust from cylinder 4 to exhaust manifold 48. In anotherexample, valve 65 may be adjusted to allow all of the exhaust gas fromcylinder 4 to intake manifold 25, while blocking any EGR flow to theexhaust manifold.

Exhaust catalyst 70 is configured as a water gas shift (WGS) catalyst.WGS catalyst 70 is configured to generate hydrogen gas from rich exhaustgas received in passage 50 from cylinder 4.

Each of cylinders 1-4 may include internal EGR by trapping exhaust gasesfrom a combustion event in the respective cylinder and allowing theexhaust gases to remain in the respective cylinder during a subsequentcombustion event. The amount of internal EGR may be varied via adjustingintake and/or exhaust valve opening and/or closing times. For example,by increasing intake and exhaust valve overlap, additional EGR may beretained in the cylinder during a subsequent combustion event. ExternalEGR is provided to cylinders 1-4 solely via exhaust flow from the secondcylinder group 18 (herein, cylinder 4) and EGR passage 50. In anotherexample, external EGR may only be provided to cylinders 1-3 and not tocylinder 4. External EGR is not provided by exhaust flow from cylinders1-3. Thus, in this example, cylinder 4 is the sole source of externalEGR for engine 10 and therefore is also referred to herein as thededicated EGR cylinder (or dedicated cylinder group). Cylinders 1-3 arealso referred to herein as a non-dedicated EGR cylinder group ornon-dedicated EGR cylinders. While the current example shows thededicated EGR cylinder group as having a single cylinder, it will beappreciated that in alternate engine configurations, the dedicated EGRcylinder group may have more engine cylinders.

EGR passage 50 may include an EGR cooler 45 for cooling EGR delivered tothe engine intake. In addition, EGR passage 50 may include a firstexhaust gas sensor 59 for estimating an air-fuel ratio of the exhaustrecirculated from the second cylinder group to the remaining enginecylinders. A second exhaust gas sensor 61 may be positioned downstreamof the exhaust manifold sections of the first cylinder group forestimating an air-fuel ratio of exhaust in the first cylinder group.Still further exhaust gas sensors may be included in the engine systemof FIG. 1.

A hydrogen concentration in external EGR from cylinder 4 may beincreased via enriching an air-fuel mixture combusted in cylinder 4. Inparticular, the amount of hydrogen gas generated at WGS catalyst 70 maybe increased by increasing the degree of richness of exhaust received inpassage 50 from cylinder 4. Additionally, a catalyst temperature may beadjusted in order to increase an efficiency of WGS catalyst 70. Thus, toprovide hydrogen enriched exhaust to engine cylinders 1-4, fueling ofthe second cylinder group 18 may be adjusted so that cylinder 4 isenriched. In one example, the hydrogen concentration of the external EGRfrom cylinder 4 may be increased during conditions when enginecombustion stability is less than desired. This action increaseshydrogen concentration in external EGR and it may improve enginecombustion stability, especially at lower engine speeds and loads (e.g.,idle). In addition, the hydrogen enriched EGR allows much higher levelsof EGR to be tolerated in the engine, as compared to conventional (lowerhydrogen concentration) EGR, before encountering any combustionstability issues. By increasing the range and amount of EGR usage,engine emissions and engine fuel economy may be improved.

Combustion chambers 30 may be supplied one or more fuels, such asgasoline, alcohol fuel blends, diesel, biodiesel, compressed naturalgas, etc. Fuel may be supplied to the combustion chambers via injector66. Fuel injector 66 may draw fuel from fuel tank 26. In the depictedexample, fuel injector 66 is configured for direct injection though inother embodiments, fuel injector 66 may be configured for port injectionor throttle valve-body injection. Further, each combustion chamber mayinclude one or more fuel injectors of different configurations to enableeach cylinder to receive fuel via direct injection, port injection,throttle valve-body injection, or combinations thereof. In thecombustion chambers, combustion may be initiated via spark ignitionand/or compression ignition.

Exhaust from exhaust manifold 48 is directed to turbine 76 to drive theturbine. When reduced turbine torque is desired, some exhaust may bedirected instead through a wastegate (not shown), by-passing theturbine. The combined flow from the turbine and the wastegate then flowsthrough emission control device 170. In general, one or more emissioncontrol devices 170 may include one or more exhaust after-treatmentcatalysts configured to catalytically treat the exhaust flow, andthereby reduce an amount of one or more substances in the exhaust flow.For example, one exhaust after-treatment catalyst may be configured totrap NO_(x) from the exhaust flow when the exhaust flow is lean, and toreduce the trapped NO_(x) when the exhaust flow is rich. In otherexamples, an exhaust after-treatment catalyst may be configured todisproportionate NO_(x) or to selectively reduce NO_(x) with the aid ofa reducing agent. In still other examples, an exhaust after-treatmentcatalyst may be configured to oxidize residual hydrocarbons and/orcarbon monoxide in the exhaust flow. Different exhaust after-treatmentcatalysts having any such functionality may be arranged in wash coats orelsewhere in the exhaust after-treatment stages, either separately ortogether. In some embodiments, the exhaust after-treatment stages mayinclude a regeneratable soot filter configured to trap and oxidize sootparticles in the exhaust flow. All or part of the treated exhaust fromemission control device 170 may be released into the atmosphere viaexhaust conduit 35.

Engine system 100 further includes a control system 14. Control system14 includes a controller 12, which may be any electronic control systemof the engine system or of the vehicle in which the engine system isinstalled. Controller 12 may be configured to make control decisionsbased at least partly on input from one or more sensors 16 within theengine system, and may control actuators 81 based on the controldecisions. For example, controller 12 may store computer-readableinstructions in memory, and actuators 81 may be controlled via executionof the instructions. Example sensors include MAP sensor 27, MAF sensor47, exhaust gas temperature and pressure sensors 128 and 129, and oxygensensors 24, and 61. Example actuators include throttle 20, fuel injector66, dedicated cylinder group valve 65, etc. Additional sensors andactuators may be included, as described in FIG. 2. Storage mediumread-only memory in controller 12 can be programmed with computerreadable data representing instructions executable by a processor forperforming the methods described below, as well as other variants thatare anticipated but not specifically listed. Example methods androutines are described herein with reference to FIGS. 4-7.

Referring to FIG. 2, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Flywheel 97 and ring gear 99 arecoupled to crankshaft 40. Starter 96 includes pinion shaft 98 and piniongear 95. Pinion shaft 98 may selectively advance pinion gear 95 toengage ring gear 99. Starter 96 may be directly mounted to the front ofthe engine or the rear of the engine. In some examples, starter 96 mayselectively supply torque to crankshaft 40 via a belt or chain.Combustion chamber 30 is shown communicating with intake manifold 44 andexhaust manifold 48 via respective intake valve 52 and exhaust valve 54.Each intake and exhaust valve may be operated by an intake cam 51 and anexhaust cam 53. The position of intake cam 51 may be determined byintake cam sensor 55. The position of exhaust cam 53 may be determinedby exhaust cam sensor 57.

Fuel injector 66 is shown positioned to inject fuel directly intocombustion chamber 30, which is known to those skilled in the art asdirect injection. Alternatively, fuel may be injected to an intake port,which is known to those skilled in the art as port injection. Fuelinjector 66 delivers liquid fuel in proportion to the pulse width ofsignal FPW from controller 12. Fuel is delivered to fuel injector 66 bya fuel system (not shown) including a fuel tank, fuel pump, and fuelrail (not shown). Fuel injector 66 is supplied operating current fromdriver 68 which responds to controller 12. In addition, intake manifold44 is shown communicating with optional electronic throttle 62 whichadjusts a position of throttle plate 64 to control air flow from airintake 42 to intake manifold 44. In one example, a low pressure directinjection system may be used, where fuel pressure can be raised toapproximately 20-30 bars. Alternatively, a high pressure, dual stage,fuel system may be used to generate higher fuel pressures. In someexamples, throttle 62 and throttle plate 64 may be positioned betweenintake valve 52 and intake manifold 44 such that throttle 62 is a portthrottle.

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 48 upstream of emission control device 170.Alternatively, a two-state exhaust gas oxygen sensor may be substitutedfor UEGO sensor 126. Emission control device 170 may be configured asdescribed above with regard to FIG. 1.

Controller 12 is shown in FIG. 2 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106, random access memory 108, keep alive memory 110, and aconventional data bus. Controller 12 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 115; a position sensor134 coupled to an accelerator pedal 130 for sensing force applied byfoot 132; a measurement of engine manifold pressure (MAP) from pressuresensor 122 coupled to intake manifold 44; an engine position sensor froma Hall effect sensor 119 sensing crankshaft 40 position; a measurementof air mass entering the engine from sensor 121; and a measurement ofthrottle position from sensor 58. Barometric pressure may also be sensed(sensor not shown) for processing by controller 12. In a preferredaspect of the present description, engine position sensor 119 produces apredetermined number of equally spaced pulses for every revolution ofthe crankshaft, from which engine speed (RPM) can be determined.

In some examples, the engine may be coupled to an electric motor/batterysystem in a hybrid vehicle as shown in FIG. 3 or a stop/start vehicleequipped with a high voltage starter system (not shown).

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 44, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g., whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC). During thecompression stroke, intake valve 52 and exhaust valve 54 are closed.Piston 36 moves toward the cylinder head so as to compress the airwithin combustion chamber 30. The point at which piston 36 is at the endof its stroke and closest to the cylinder head (e.g., when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top dead center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by ignition devices such as spark plug 92, resulting incombustion. During the expansion stroke, the expanding gases push piston36 back to BDC. Crankshaft 40 converts piston movement into a rotationaltorque of the rotary shaft. Finally, during the exhaust stroke, theexhaust valve 54 opens to release the combusted air-fuel mixture toexhaust manifold 48 and the piston returns to TDC. Note that the abovedescription is merely an example, and that intake and exhaust valveopening and/or closing timings may vary, such as to provide positive ornegative valve overlap, late intake valve closing, or various otherexamples.

FIG. 3 depicts a hybrid propulsion system 300 for a vehicle. In thedepicted embodiment, the vehicle is a hybrid electric vehicle (HEV). Forsimplicity and clarity, the description herein will focus on controllingengine operation with one or more DEGR cylinders in a HEV, however itshould be understood that the use of a HEV for this description is notmeant to be limiting in any way. For example, the methods depictedherein may be applied to controlling engine operation with one or moreDEGR cylinders in a flywheel hybrid, where a mechanical flywheel storagedevice is used instead of an electric battery, or a hydraulic hybrid,where energy is stored in a pressure accumulator instead of an electricbattery, without departing from the scope of the present disclosure.

Propulsion system 300 includes an internal combustion engine 10 having aplurality of cylinders 30. Fuel may be provided to each cylinder ofengine 10 from a fuel system (not shown) including one or more fueltanks, one or more fuel pumps, and injectors 66.

Engine 10 delivers power to transmission 344 via torque input shaft 318.In the depicted example, transmission 344 is a power-split transmission(or transaxle) that includes a planetary gearset 322 and one or morerotating gear elements. Transmission 344 further includes an electricgenerator 324 and an electric motor 326. The electric generator 324 andthe electric motor 326 may also be referred to as electric machines aseach may operate as either a motor or a generator. Torque is output fromtransmission 344, for propelling vehicle tractions wheels 352, via apower transfer gearing 334, a torque output shaft 319, anddifferential-and-axle assembly 336.

Generator 324 is drivably connected to electric motor 326 such that eachof electric generator 324 and electric motor 326 may be operated usingelectric energy from an electrical energy storage device, hereindepicted as battery 354. In some embodiments, an energy conversiondevice, such as an inverter, may be coupled between the battery and themotor to convert the DC output of the battery into an AC output for useby motor. However, in alternate embodiments, the inverter may beconfigured in the electric motor.

Electric motor 326 may be operated in a regenerative mode, that is, as agenerator, to absorb energy from vehicle motion and/or the engine andconvert the absorbed kinetic energy to an energy form suitable forstorage in battery 354. Furthermore, electric motor 326 may be operatedas a motor or generator, as required, to augment or absorb torqueprovided by the engine.

Planetary gearset 322 comprises a ring gear 342, a sun gear 343, and aplanetary carrier assembly 346. The ring gear and sun gear may becoupled to each other via the carrier. A first input side of planetarygearset 322 is coupled to engine 10 while a second input side of theplanetary gearset 322 is coupled to the generator 324. An output side ofthe planetary gearset is coupled to vehicle traction wheels 352 viapower transfer gearing 334 including one or more meshing gear elements360-368. In one example, the meshing gear elements 360-368 may be stepratio gears wherein carrier assembly 346 may distribute torque to thestep ratio gears. Gear elements 362, 364, and 366 are mounted on acountershaft 317 with gear element 364 engaging an electric motor-drivengear element 370. Electric motor 326 drives gear element 370, which actsas a torque input for the countershaft gearing. In this way, theplanetary carrier 346 (and consequently the engine and generator) may becoupled to the vehicle wheels and the motor via one or more gearelements. Hybrid propulsion system 300 may be operated in variousembodiments including a full hybrid system, wherein the vehicle isdriven by only the engine and generator cooperatively, only the electricmotor, or a combination. Alternatively, assist or mild hybridembodiments may also be employed, wherein the engine is the primarysource of torque and the electric motor selectively adds torque duringspecific conditions, such as during a tip-in event.

For example, the vehicle may be driven in an engine mode wherein engine10 is operated in conjunction with the electric generator (whichprovides reaction torque to the planetary gear-set and allows a netplanetary output torque for propulsion) and used as the primary sourceof torque for powering wheels 352 (the generator may also be providingtorque to wheels if in motoring mode). During the engine mode, fuel maybe supplied to engine 10 from a fuel tank via fuel injector 66 so thatthe engine can spin fueled to provide the torque for propelling thevehicle. Specifically, engine power is delivered to the ring gear of theplanetary gearset. Coincidentally, the generator provides torque to thesun gear 343, producing a reaction torque to the engine. Consequently,torque is output by the planetary carrier to gears 362, 364, 366 oncountershaft 317, which in turn delivers the power to wheels 352.Additionally, the engine can be operated to output more torque than isneeded for propulsion, in which case the additional power is absorbed bythe generator (in generating mode) to charge the battery 354 or supplyelectrical power for other vehicle loads.

In another example, the vehicle may be driven in an assist mode whereinengine 10 is operated and used as the primary source of torque forpowering wheels 352 and the electric motor is used as an additionaltorque source to act in cooperation with, and supplement the torqueprovided by, engine 10. During the assist mode, as in the engine mode,fuel is supplied to engine 10 so as to spin the engine fueled andprovide torque to the vehicle wheels.

In still another example, the vehicle may be driven in an engine-off orelectric mode wherein battery-powered electric motor 326 is operated andused as the only source of torque for driving wheels 352. As such,during the electric mode, no fuel may be injected into engine 10irrespective of whether the engine is spinning or not. The electric modemay be employed, for example, during braking, low speeds, low loads,while stopped at traffic lights, etc. Specifically, motor power isdelivered to gear element 370, which in turn drives the gear elements oncountershaft 317, and thereon drives wheels 352.

Propulsion system 300 may further include a control system includingcontroller 12 configured to receive information from a plurality ofsensors 16 (various examples of which are described herein) and sendingcontrol signals to a plurality of actuators 81 (various examples ofwhich are described herein). As one example, sensors 16 may includevarious pressure and temperature sensors, a fuel level sensor, variousexhaust gas sensors, etc. The various actuators may include, forexample, the gear set, cylinder fuel injectors (not shown), an airintake throttle coupled to the engine intake manifold (not shown), etc.Additional sensors and actuators are elaborated in FIGS. 1-2. Controller12 may receive input data from the various sensors, process the inputdata, and trigger the actuators in response to the processed input databased on instruction or code programmed therein corresponding to one ormore routines. Example control routines are described herein with regardto FIG. 4-7.

Turning now to FIG. 4, a flow chart for a high level example method 400for operating a hybrid vehicle engine where the engine comprises one ormore dedicated EGR (DEGR) cylinders is shown. More specifically, method400 may be used to indicate whether a tip-out event is indicated, or ifthe vehicle is operating under low-load, where continued engineoperation with DEGR is not desirable due to combustion stability issues.Responsive to low-load conditions where a tip-out event is notindicated, if battery state of charge is greater than a threshold and ifengine operation is not required, the vehicle may be propelled viabattery power while discontinuing engine operation. Alternatively, ifbattery state of charge is lower than a threshold, engine operation maybe continued, engine load may be increased (or during a partial tipout,not decreased all the way to the load and speed required for thedecreasing wheel power), and excess torque used to charge the battery.In this way, under circumstances where the unmitigated continuedoperation of an engine configured with one or more DEGR cylinders is notdesirable, actions may be taken such that combustion stability issuesmay be avoided. By combining a dedicated EGR engine with a hybridpowertrain, fuel economy may thus be improved, while avoiding theproblems associated with dedicated EGR at low loads. Method 400 will bedescribed with reference to the systems described herein and shown inFIGS. 1-3, though it should be understood that similar methods may beapplied to other systems without departing from the scope of thisdisclosure. Method 400 may be carried out by a controller, such ascontroller 12 in FIG. 1, and may be stored at the controller asexecutable instructions in non-transitory memory. Instructions forcarrying out method 400 and the rest of the methods included herein maybe executed by the controller based on instructions stored on a memoryof the controller and in conjunction with signals received from sensorsof the engine system, such as the sensors described above with referenceto FIGS. 1-3. The controller may employ fuel system actuators such asfuel injectors (e.g., 66), spark plug (e.g., 92), intake throttle (e.g.,20), etc., according to the method below.

Method 400 begins at 402 and includes estimating and/or measuring engineoperating conditions and vehicle operating parameters. For example,brake pedal position, accelerator pedal position, operator torquedemand, battery state of charge (SOC), engine temperature (Teng),ambient temperature and humidity, barometric pressure (BP), etc., may beestimated and/or measured. In one example the hybrid vehicle system is apowersplit hybrid. However, as described above with regard to FIG. 3, inother examples the hybrid vehicle system may comprise a flywheel hybrid,or a hydraulic hybrid, without departing from the scope of the presentdisclosure.

Proceeding to 404, a vehicle mode of operation may be determined basedon the estimated operating conditions. For example, based at least onthe estimated driver torque demand and the battery SOC, it may bedetermined whether the vehicle is to be operated in an engine-only mode(with the engine driving the vehicle wheels), an assist mode (with thebattery assisting the engine in driving the vehicle), or anelectric-only mode (with only the battery driving the vehicle). In oneexample, if the demanded torque can be provided by only the battery, asdiscussed in more detail below, the vehicle may be operated in theelectric-only mode. In another example, if the demanded torque cannot beprovided solely by the battery, the vehicle may be operated in theengine mode, or in the assist mode. The vehicle may accordingly beoperated in the determined mode of operation.

Continuing to 406, it may be confirmed whether the vehicle is in anengine-on mode. For example, it may be confirmed that the vehicle isoperating in an engine-only mode where the vehicle is being propelledwith engine torque only. Alternatively, it may be confirmed that thevehicle is operating in an assist mode and that the vehicle is beingpropelled, as least in part, with engine torque. If the engine-on modeis not confirmed, method 400 may proceed o 408. At 408, method 400 mayinclude indicating whether engine restart conditions are met. Forexample, engine restart conditions may be met responsive to one or moreof the battery SOC being lower than a threshold level of a charge, arequest for passenger heat or air conditioning being received, operatortorque demand being greater than a threshold amount, etc. If enginerestart conditions are not met at 408, method 400 may proceed to 409. At409, method 400 may include maintaining the current vehicle operationalstatus. For example, the engine may be maintained shut down and thevehicle may be continued to be operated via battery power. In anotherexample, if the vehicle is not in operation, for example the vehicle isin a key-off state, the engine may similarly be maintained shutdownuntil restart conditions are met. Alternatively, if at 408 it isindicated that restart conditions are met, method 400 may proceed tomethod 500 depicted in FIG. 5 where it may be determined whether theengine restart event comprises a hot start, or a cold start event, whereengine operation during the restart may be adjusted as described infurther detail below.

Returning to 406, if it is indicated that the vehicle is in an engine-onmode, method 400 may proceed to 410. At 410, method 400 may includeindicating whether a tip-out event is indicated. A tip-out eventindicates that less power or vehicle deceleration is demanded by thedriver, and may be indicated by braking the vehicle, lifting off of thegas pedal, or a combination of braking and/or lifting off of the gaspedal. If a tip-out event is indicated, method 400 may proceed to method600 depicted in FIG. 6, where an engine shutdown may be conducted inorder to avoid a rapid percent increase in EGR in the intake manifold.

If, at 410, a tip-out event is not indicated, method 400 may proceed to412. At 412, method 400 may include indicating whether engine torquedemand is less than a threshold torque demand (preselected load). Forexample, the threshold torque demand may comprise an engine load where adedicated amount of EGR may result in combustion stability issues. Thethreshold torque demand may comprise a level of torque greater than thatof a tip-out event, by a predetermined amount. As such, a level oftorque may be requested by a vehicle operator that is below thethreshold torque demand, but greater than a tip-out event. Furthermore,transitioning to a level of torque demand below the threshold torquedemand may be more gradual than the transition in torque demand thatoccurs responsive to a tip-out event.

If, at 412, engine torque demand is not less than the threshold torquedemand, and a tip-out event was not indicated at 410, method 400 mayproceed to 414. At 414, method 400 may include maintaining engineoperation parameters. For example, if the vehicle is operating in anengine-only mode where the vehicle is being propelled with engine torqueonly, the vehicle may be maintained in such an operational status.Alternatively, if the vehicle is operating in an assist mode wherein thevehicle is operating, at least in part, by engine torque, the vehiclemay be maintained in such an operational status. Furthermore, while thevehicle is operating in an engine-on mode, the vehicle may becontinually monitored for whether a tip-out event is indicated, orwhether an engine torque demand has dropped below the threshold torquedemand.

If, at 412, engine torque demand is indicated to be below the thresholdtorque demand, method 400 may proceed to 416. As described brieflyabove, if engine torque demand drops below a threshold torque demand,continued operation of the engine with dedicated EGR may lead tocombustion stability issues. As such, in a hybrid vehicle, mitigatingactions may be taken to prevent issues associated with continued engineoperation with dedicated EGR when engine torque demand is below athreshold torque demand. Accordingly, at 416, method 400 may includeestimating and/or measuring the battery SOC (energy storage capacity),and comparing the estimated and/or measured SOC to a threshold chargelevel (predetermined amount). If the hybrid vehicle comprises a flywheelhybrid, or a hydraulic hybrid, at 416, method 400 may include estimatingand/or measuring an energy level stored in a flywheel, or an amount ofpressure accumulation, and comparing respective energy/pressure levelsto their respective threshold charge levels. In the example describedherein comprising a HEV, the threshold charge may be defined as abattery state of charge wherein the battery is not capable of acceptingfurther charge. If, at 416, it is indicated that the battery SOC isgreater than the threshold charge level, method 400 may proceed to 418.

At 418, it may be indicated whether engine operation is required. Insome examples, engine operation may be required if a vehicle operatorhas requested vehicle cabin heat, or vehicle cabin air-conditioning. Ifengine operation is required, method 400 may proceed to method 700depicted in FIG. 7, and may include turning off the fuel injector forthe DEGR cylinder, as described in further detail therein.Alternatively, if engine operation is not indicated to be required at418, method 400 may proceed to 420.

At 420, method 400 may include disabling fueling of the engine.Disabling engine fueling at 420 may comprise stopping fuel injection tothe engine cylinders, and discontinuing spark. Furthermore, at 420, themotor/generator of the hybrid vehicle system may be operated. As such,the vehicle may be propelled using motor torque instead of enginetorque, wholly by energy from the energy storage device (e.g., battery).By propelling the vehicle by using motor torque, combustion instabilityissues may be avoided at torque demands below the threshold torquedemand. As described above, in the case of a flywheel hybrid, or ahydraulic hybrid, torque may be provided via energy stored in aflywheel, or via energy stored in a pressure accumulator, respectively,instead of via energy stored in a battery. For simplicity, furtherreference to flywheel and/or hydraulic hybrid technology will beavoided, instead reference will be made to hybrid electric vehicles.However, it should be understood that any example depicted below mayinclude flywheel hybrid, or hydraulic hybrid technology withoutdeparting from the scope of this disclosure. Proceeding to 422, toexpedite the purging of remaining EGR in the intake manifold, method 400includes spinning the engine unfueled via the motor/generator. Forexample, the engine may be spun unfueled for an additional 1-3 secondsvia the motor/generator. In addition, where air supplied to the intakemanifold is regulated by an intake throttle, the intake throttle in theintake passage may be fully opened. By opening the intake throttle fullyduring the spinning, the dedicated EGR system and the air inductionsystem may be purged of exhaust residuals and replenished with freshintake air. By purging the air induction system and EGR system ofexhaust residuals, combustion stability issues associated with asubsequent restart of the engine may be avoided.

Spinning the engine unfueled via the motor includes operating thegenerator using electrical energy from the system battery to spin theengine at a selected engine speed. The engine may be spun unfueled at aselected engine speed that is based on the engine speed before the fuelinjectors are shut-off. For example, the controller may operate thegenerator to maintain the engine speed that the engine was spinning atimmediately before the fuel injectors were disabled. As another example,the generator may spin the engine unfueled at an engine speed that is afunction (e.g., fraction) of the engine speed that the engine wasspinning at immediately before the fuel injectors were disabled.Alternatively, the selected engine speed may be a speed that isefficient for both the engine and the transmission. As such, the purgetime required to completely purge the EGR will be a function of enginespeed and throttle position.

In an alternate example, the engine may be spun unfueled at a speedbased on the vehicle speed. For example, the engine speed may be set tobe a calibratable speed that is stored in the controller's memory in alook-up table accessed as a function of the vehicle speed. In yetanother example, the engine may be spun at a speed based on the vehiclespeed and a rotational speed (or rotational speed limit) of the rotatingcomponents of the planetary gear transmission. Motor/generator settingsmay be adjusted to enable the engine to be spun, via motor torque, atthe selected engine speed. In some embodiments, each of the generatorand the motor may be operated to spin the engine at the selected enginespeed. In other embodiments, only the generator may need to be operated.

In yet another example, the engine may be spun unfueled at an enginespeed corresponding to at least a cranking speed of the engine. Inaddition to expediting EGR purging, this allows the engine to be rapidlyrestarted in the event of a driver change-of-mind operation (such aswhere the operator increases demanded engine torque shortly after theengine torque demand falls below the threshold). For example, inresponse to an indication of an operator change of mind, the controllermay start to fuel the engine and spin up the engine from the crankingspeed so as to meet operator torque demand.

In still other examples, the engine may be spun unfueled at an enginespeed that allows the EGR to be purged as fast as possible. Herein, theengine speed may be selected based on the intake EGR level at a time ofthe decreasing engine torque demand (e.g., at a time of operator pedaltip-out). For example, the engine speed may be transiently raised to amaximum allowable engine speed that does not affect torque output butthat allows EGR to be purged as fast as possible. In yet anotherexample, the engine may be spun unfueled at an engine speed that allowsthe EGR to be purged at a slower rate.

In further examples, instead of spinning the engine continuously untilEGR is purged, the engine may be spun unfueled via the generatorintermittently. For example, during a downhill travel, the engine may bepulsed unfueled via the generator to purge the EGR.

At 424, method 400 includes indicating whether the EGR has beensufficiently purged from the engine intake manifold. For example, it maybe determined if EGR (flow, amount, concentration, level, etc.) in theintake is lower than a threshold. In one example, an intake oxygensensor, such as sensor 24 of FIG. 1, may be used to estimate theconcentration of EGR in the intake. Therein, a drop in intake oxygenconcentration may be used to infer an increase in EGR dilution delivery.In one example, the threshold may be based on EGR tolerance of theengine at low engine load conditions.

If the EGR is not lower than the threshold, then the controller maycontinue to spin the engine unfueled via the motor/generator until EGRis sufficiently purged. If EGR is lower than the threshold, then at 426,the routine includes spinning the engine to rest. For example, theengine may be spun to rest via the motor/generator and thereafter theengine may be maintained shutdown until engine restart conditions aremet. In the meantime, the vehicle may continue to be propelled usingmotor torque. As such, this allows the EGR rate to be reset (forexample, to zero) such that when the engine is restarted, combustionstability issues may not be exacerbated by residual EGR in the engineintake.

Continuing to 428, as described above with regard to step 408 of method400, restart conditions may be met responsive to battery SOC below athreshold charge level, a heat or air conditioning request, torquedemand greater than a threshold amount, etc. In one example, duringpropelling the vehicle via motor torque, responsive to an indicationthat the charge state of the battery exceeds a threshold charge level(e.g., predetermined value, or second threshold SOC), restart conditionsmay include ceasing the vehicle propulsion from the battery (or otherenergy storage device), and resuming fueling (and spark) the one or morecylinders that recirculate exhaust gas to the remaining cylinders whileengine load may be quickly increased above the threshold torque demandby charging the system battery according to the method depicted in FIG.4, and further described in FIG. 8.

If engine restart conditions are not met, method 400 may includemaintaining the vehicle operational status, which may include continuingto propel the vehicle via motor torque, or if at some point a vehicleoff event is detected, maintaining the engine off during the vehicle offcondition until engine restart conditions are met.

If restart conditions are met at 428, method 400 may proceed to method500, depicted in FIG. 5 where it may be determined whether the enginerestart event comprises a hot start, or a cold start event, where engineoperation during the restart may be adjusted as described in furtherdetail below.

Returning to 416, if battery SOC is indicated to be lower than thethreshold charge level, then it may be determined that the battery iscapable of accepting further charge. Consequently, at 430, method 400may include continuing engine operation fueled with engine output torquehigher than demanded torque. As such, the system battery may be chargedby the engine output torque greater than demanded torque. Charging thebattery may include operating the generator using the excess engineoutput torque, the generator coupled to the battery. For example, theengine may be operated at a level of torque and load where dedicated EGRdoes not result in combustion instability issues. The level of torquemay be a predetermined threshold level of torque, in some examples.

Proceeding to 432, while the engine is being operated at a level oftorque higher than demanded torque with excess torque used to charge thebattery, battery SOC may be monitored. If, at 432, battery SOC isindicated to reach a threshold battery SOC, the threshold SOC comprisinga level of charge where the battery is unable to accept further charge,method 400 may proceed to 418 and may include indicating whether engineoperation is required. As described above, engine operation may berequired if the vehicle operator has requested heat, or airconditioning, for example. If engine operation is required, method 400may proceed to method 700, where fueling of the DEGR cylinder may bestopped, as described in further detail therein. If engine operation isnot indicated to be required at 418, method 400 may proceed to 420, andmay include disabling fueling (and spark) of the engine, and propellingthe vehicle using motor torque instead of engine torque. Followingdisabling fueling to the engine at 420, method 400 may proceed asdescribed above. In an effort to avoid redundancy, each step of themethod will not be reiterated in full detail here, but it may beunderstood that each step continuing from 420 may comprise all aspectsof method 400 described in detail above. Briefly, propelling the vehicleusing motor torque may avoid combustion instability issues at torquedemands below the threshold torque level, when battery charge hasincreased to a level where further charging is not possible. In order toquickly purge remaining EGR in the intake manifold, the engine may bespun unfueled with the intake throttle fully open, to replenish thededicated EGR system and air induction system with fresh intake air.Responsive to an indication that the EGR has been sufficiently purgedfrom the engine intake manifold, the engine may be spun to rest via themotor and thereafter maintained shutdown until engine restart conditionsare met. If engine restart conditions are met, method 400 may proceed tomethod 500, depicted in FIG. 5, where it may be determined whether theengine restart event comprises a hot start, or a cold start event, whereengine operation during the restart may be adjusted as described infurther detail below.

Returning to 432, if it is indicated that battery SOC has not reached athreshold SOC where the battery is unable to accept further chargeduring operating the engine at a torque level higher than torque demandwhile charging the battery, method 400 may proceed to 434. At 434,method 400 may include indicating whether engine torque demand remainsless than a threshold. For example, the threshold level may comprise thethreshold level described with regard to step 412 of method 400. Inother words, the threshold torque demand may comprise a level of torquewhere dedicated EGR may result in combustion stability issues. If theengine torque demand remains below the threshold, the engine may becontinued to be spun fueled at a torque level higher than torque demandwhile charging the battery. However, if engine torque demand remainsbelow the threshold and a tip-out event is indicated at 435, method 400may proceed to method 600, as described above. Alternatively, if at 434it is indicated that engine torque demand has risen above the thresholdamount, method 400 may proceed to 436. At 436, method 400 may includeresuming default engine operating conditions. For example, responsive toengine torque increasing above the threshold, the engine may be operatedat the torque level demand, without excess torque provided to charge thebattery. Method 400 may then end.

Turning now to FIG. 5, a flow chart for a high level example method 500for adjusting engine operation during an engine restart event, is shown.More specifically, method 500 may continue from method 400, method 600,or method 700, and includes determining whether the engine restart eventcomprises a hot start event, or a cold start event, and differentiallyregulating vehicle operating conditions depending on the type of enginerestart event. For example, responsive to a hot start event,non-dedicated EGR cylinders may initially be activated, followed byactivation of the one or more DEGR cylinders responsive to an indicationof stable engine speed and load above defined thresholds. Alternatively,responsive to a cold-start event, non-dedicated EGR cylinders mayinitially be activated, followed by activation of the one or more DEGRcylinders responsive to an indication of stable engine speed above athreshold, where engine load is maintained above a threshold load limitfor dedicated EGR operation by using excess torque to charge the batteryduring an engine warm-up period. Method 500 will be described withreference to the systems described herein and shown in FIGS. 1-3, thoughit should be understood that similar methods may be applied to othersystems without departing from the scope of this disclosure. Method 500may be carried out by a controller, such as controller 12 in FIG. 1, andmay be stored at the controller as executable instructions innon-transitory memory. Instructions for carrying out method 500 and therest of the methods included herein may be executed by the controllerbased on instructions stored on a memory of the controller and inconjunction with signals received from sensors of the engine system,such as the sensors described above with reference to FIGS. 1-3. Thecontroller may employ fuel system actuators such as fuel injectors(e.g., 66), spark plug (e.g., 92), etc., according to the method below.

Method 500 begins at 505 and includes estimating and/or measuringvehicle operating conditions. Vehicle operating conditions may includebut are not limited to engine speed, accelerator position, throttleposition, brake pedal position, vehicle speed, engine temperature, andload. At 510, method 500 includes indicating whether the engine restartevent comprises a hot start, or a cold start event. For example, at 510,indicating an engine cold start may include engine temperature (orengine coolant temperature) being lower than a threshold temperature(such as a catalyst light-off temperature). If cold start conditions arenot confirmed, then it may be determined that the engine is in a hotstart condition, and method 500 may proceed to 515. More specifically, ahot start condition may comprise a determination that temperature of oneor more catalyst(s) coupled to exhaust from the non-DEGR cylinders is ator above a predetermined temperature, that a time since last enginestart is less than a preselected time, an indication exhaust gastemperatures are above a predetermined value, or, temperature of acoolant coupled to the engine is above a threshold value.

At 515, method 500 may include operating non-DEGR cylinders based on theestimated operating conditions and not operating DEGR cylinders.Non-DEGR cylinders may be operated by actuating the valves of thenon-DEGR cylinders, and supplying fuel and spark to the non-DEGRcylinders for combustion. In some examples, during a stop-startoperation of the engine, when the engine is restarted, the non-DEGRcylinders may be operated such that an engine air-to-fuel ratio isricher than stoichiometry in order to regenerate or activate an exhaustemission control device, such as emission control device 170 at FIG. 1.

Proceeding to 520, method 500 may include monitoring engine speed duringa run-up period (e.g., a time from when engine speed is zero until theengine reaches a stable speed). Further, engine speed may be monitoredfor a predetermined amount of time after engine speed reaches stablespeed during an engine start. Monitoring engine speed may includecomparing actual engine speed against a desired engine speed trajectorythat is stored in controller memory. Method 500 proceeds to 525 aftermonitoring engine speed. At 525, method 500 indicates whether or not theengine speed is greater than a threshold speed, and whether or not arate of change of engine speed is less than a threshold change. In otherwords, method 500 indicates if engine speed has reached a stable speedsince engine start. In some examples, a coolant temperature, an ambienttemperature, and a catalyst temperature may be utilized in addition toengine speed to determine stable engine operation conditions. If at 525,it is determined that the engine speed is less than the threshold speed,and rate of change is greater than the threshold change, method 500 mayproceed to 530. At 530, the method may continue engine operation withoperating non-DEGR cylinders and without operating DEGR cylinders untilthe engine speed reaches the threshold speed and the rate of change ofspeed is less than threshold rate. If, at 525, it is determined thatengine speed is greater than the threshold speed, and the rate of changein engine speed is less than the threshold rate of change, method 500may proceed to 535. At 535, method 500 may include indicating whetherengine torque demand is less than a threshold torque demand. Forexample, as described above, the threshold torque demand may comprise anengine load where a dedicated amount of EGR may result in combustionstability issues. If engine torque demand is less than a thresholdtorque demand, method 500 may proceed to 530 and may include continuingengine operation with operating non-DEGR cylinders and without operatingDEGR cylinders, as described above. However, if at 535 it is indicatedthat engine torque demand is greater than the threshold torque demand,method 535 may proceed to 536, and may include activating the DEGRcylinder(s). As such, DEGR cylinders may be activated by actuating theintake/exhaust valves, and supplying fuel and spark to the cylinder forcombustion. Fuel to the DEGR cylinders and the non-DEGR cylinders may beadjusted such that the engine air-to-fuel ratio is stoichiometric. Insome examples, prior to activating the DEGR cylinder, method 500 mayinclude using the electric motor for high frequency cancellation oftorque pulsations resulting from the imbalance between torque producedfrom the combusting non-DEGR cylinders, and torque from thenon-combusting DEGR cylinder. For example, the motor may be controlledto supply torque to the driveline of the vehicle to provide asubstantially similar level of torque as previous and/or subsequentfiring cylinders. As such, noise, vibration, and harshness may bemitigated during engine startup events.

In another example, described here and depicted in further detail inFIG. 8, responsive to a hot start event, instead of operating thenon-DEGR cylinders followed by activation of the DEGR cylinder(s)responsive to an indication of stable engine speed and load abovedefined thresholds, an alternative methodology may be employed. In oneexample, responsive to a hot start event, both non-DEGR cylinders andDEGR cylinders may be activated concurrently, while engine load may bequickly increased above the threshold torque demand by charging a systembattery, where the threshold torque demand may comprise an engine loadwhere a dedicated amount of EGR may result in combustion stabilityissues as described above. In doing so, combustion stability issues maybe avoided, and NOx emissions reduced during a hot start event. In suchan example, engine load may be maintained above the threshold torquedemand by charging the energy storage device until it is indicated thatdriver demanded torque is above the threshold torque demand, at whichpoint the engine may be operated at the torque level demand, withoutexcess torque provided to charge the battery, as described above withregard to FIG. 4. Furthermore, in such an example, prior to activatingthe non-DEGR cylinders and DEGR cylinders concurrently, it may beindicated whether battery SOC is below a threshold, such that thebattery can accept further charge. If it is indicated that the batteryis unable to accept further charge, then the method may proceed asdepicted in FIG. 5, by operating the non-DEGR cylinders followed byactivation of the DEGR cylinders, as described.

Returning to 510, if cold start conditions are confirmed, method 500 mayproceed to 540. At 540, method 500 may include operating non-DEGRcylinder(s) based on the estimated operating conditions and notoperating DEGR cylinders. As described above, non-DEGR cylinders may beoperated by actuating the valves of the non-DEGR cylinders and supplyingfuel and spark to the non-DEGR cylinders for combustion, and in someexamples (e.g., start-stop operation), the non-DEGR cylinders may beoperated such that engine air-to-fuel ratio is richer than stoichiometryin order to regenerate or activate an exhaust emission control device.

Proceeding to 545, method 500 may include monitoring engine speed duringa run-up period, as described above, and may include comparing actualengine speed against a desired engine speed trajectory that is stored incontroller memory. At 550, method 500 may include indicating whetherengine speed is greater than a threshold speed, and whether or not arate of change of engine speed is less than a threshold change. In otherwords, as described above, it may be determined whether engine speed hasreached a stable speed. Coolant temperature, an ambient temperature, anda catalyst temperature may additionally be utilized to determine stableengine operating conditions. If a stable speed is not reached, method500 may continue engine operation with non-DEGR cylinders and withoutDEGR cylinder operation until the engine speed reaches the thresholdspeed and the rate of change of speed is less than the threshold rate.

If it is determined that the engine speed has reached a stable speed,method 500 may proceed to 555. At 555, method 500 includes indicatingwhether a battery state of charge (SOC) is greater than a thresholdcharge level. As one example, the threshold charge level may be definedas a battery SOC wherein the battery is not capable of accepting furthercharge, as described above with regard to FIG. 4. If, at 555, it isindicated that the battery SOC is not greater than the threshold chargelevel, method 500 may proceed to 560. At 560, method 500 may includeoperating the engine fueled via the non-DEGR cylinders with engineoutput torque above a threshold, wherein the engine output torquethreshold may be a predetermined threshold level of engine outputtorque. In one example, the level of engine output torque may comprise alevel of torque where dedicated EGR does not result in combustionstability issues. Accordingly, the system battery may be charged by theengine output torque greater than demanded torque, and may includeoperating the generator, the generator coupled to the battery. Asdescribed above, during operating the non-DEGR cylinders, to reducenoise, vibration, and harshness, the electric motor may be used forhigh-frequency cancellation of torque pulsations resulting from theimbalance between torque produced from combusting non-DEGR cylinders,and non-combusting DEGR cylinders. As such, the motor may be controlledto supply torque to the driveline of the vehicle to provide asubstantially similar level of torque as previous and/or subsequentfiring cylinders.

Responsive to increasing engine output torque to the threshold level,method 500 may proceed to 565 where method 500 includes activating theDEGR cylinder. The DEGR cylinder may be activated by actuating theintake/exhaust valves, and supplying fuel and spark to the cylinder forcombustion, and fuel to the DEGR cylinder(s) and non-DEGR cylinders maybe adjusted such that the engine air-to-fuel ratio is stoichiometric. Byactivating the DEGR cylinder when the engine output torque is at orabove the threshold level, combustion stability issues may be avoidedduring cold-start events.

Method 500 may continue to operate the engine with an output torqueabove the threshold level while charging the system battery until driverdemanded engine torque reaches or exceeds the engine output torquethreshold level. Accordingly, at 570, method 500 may include indicatingwhether the driver demanded engine torque is equal to or greater thanthe threshold level. If, at 570, it is indicated that driver demandedengine torque is not equal to or greater than the threshold level,method 500 may proceed to 575 where method 500 includes maintainingoperating the engine with engine output torque above the threshold, withthe excess torque used to charge the system battery, as described above.If, at 570, engine torque demand is equal to or greater than thethreshold level, method 500 may proceed to 580. At 580, method 500 mayinclude resuming default engine operating conditions. For example, asdescribed above, responsive to engine torque demand increasing above thethreshold level, the engine may be operated at the torque level demand,with both non-DEGR cylinders and DEGR cylinders activated, without anyexcess torque provided to charge the battery.

While not explicitly indicated in method 500, it may be understood thatfollowing activation of the DEGR cylinder after increasing engine torqueabove the threshold and charging the battery with the excess torque, ifbattery SOC increases above a threshold where the battery cannot acceptfurther charge, the excess torque engine output torque may bediscontinued and the DEGR valve deactivated. In such a circumstance, theengine may be continued to be operated without DEGR until driverdemanded engine torque increases above a threshold where DEGR does notnegatively impact combustion stability.

Accordingly, returning to 555, if it is indicated that battery SOC isabove the threshold level subsequent to an indication that engine speedhas reached a stable speed, method 500 may proceed to 585, and mayinclude maintaining the DEGR cylinder deactivated and operating theengine fueled with the non-DEGR cylinders until driver demanded torqueincreases above the threshold where DEGR does not negatively impactcombustion stability, whereupon method 500 may proceed to 590 and mayinclude activating the DEGR cylinder and resuming default engineoperating conditions.

In another example, described here and depicted in further detail inFIG. 8, responsive to a cold start event, the non-DEGR cylinders may beactivated by starting fueling, providing spark, and activating theintake and exhaust valves. However, fueling and spark (e.g., ignitiontiming) to the DEGR cylinder may be shut off while the intake andexhaust valves on the DEGR cylinder may be activated. In such an examplecold start condition, the catalyst material in an emission controldevice may not be at a sufficient temperature (e.g., light-offtemperature) in order to sufficiently process exhaust emissions. Assuch, it may be desirable to rapidly raise the temperature of thecatalyst material, thus decreasing the light-off time of one or morecatalysts coupled to the non-DEGR cylinders. By activating the non-DEGRcylinders, and activating the intake and exhaust valves on the DEGRcylinder while disabling fueling and spark to the DEGR cylinder, air maybe routed to the intake of the non-DEGR cylinders instead of exhaust,thus resulting in exhaust gases lean of stoichiometry. In such anexample, spark timing and fuel injection to the non-DEGR cylinders(e.g., remaining cylinders) may be adjusted to account for the airinstead of exhaust. With exhaust gases lean of stoichiometry, excessoxygen in the exhaust gases may all be used to light-off the catalyst.Furthermore, during such an example cold-start event, ignition to thenon-DEGR cylinders may be retarded, which may result in an increase intemperature of the exhaust gases traveling to the catalyst material. Assuch, by operating the engine lean of stoichiometry via operating theDEGR cylinder as an air pump to route air to the intake of the non-DEGRcylinders, and retarding ignition to the non-DEGR cylinders, catalystlight-off time may be decreased, which may thus reduce undesiredemissions during a cold start event.

During such an example cold start event, temperature of the catalyst maybe monitored, for example via a direct temperature measurement of theone or more catalyst(s), via temperature of a coolant coupled to theengine, time since the engine was last running, a determination ofexhaust temperature based on engine running conditions such as load,speed, air/fuel ratio, spark timing, etc. In one example, responsive toan indication that temperature of the one or more catalysts is above apredetermined threshold temperature needed for catalytic activity, andfurther responsive to an indication that an engine speed is greater thana threshold speed and has reached a stable speed, fueling and spark tothe DEGR cylinder may be initiated. In such an example, if a driverdemanded engine torque is below the engine output torque threshold levelupon an indication that the catalyst is above the predeterminedthreshold, it may be determined whether battery state of charge (SOC) isgreater than a threshold level, wherein the threshold charge level maycomprise a condition where the battery in not capable of acceptingfurther charge, as described above. If battery SOC is not greater thanthe threshold charge level, engine output torque may be increased abovethe engine output torque threshold by applying negative torque to theengine, and charging the system battery. The engine may be operated atthe engine output torque threshold level by charging the system batteryuntil it is indicated that driver demanded engine torque is equal to orgreater than the engine output torque threshold. Responsive to driverdemanded engine torque equaling or exceeding the engine output torquethreshold, default engine operating conditions may be resumed. Forexample, as described above, the engine may be operated at the torquelevel demand, with both non-DEGR cylinders and DEGR cylinders activated,without any excess torque provided to charge the battery.

However, in a condition wherein battery SOC is greater than thethreshold charge level, where temperature of the one or more catalystsis above the predetermined threshold temperature needed for catalyticactivity, yet driver demanded engine torque is below the engine outputtorque threshold, fueling and spark to the DEGR cylinder may bemaintained off, and the intake and exhaust valves on the DEGR cylindermay be deactivated. For example, deactivation of the intake and exhaustvalves may include configuring the intake and exhaust valves on the DEGRcylinder both in a closed conformation. In such an example condition,closing the intake and exhaust valves may prevent air from being routedto the intake of the non-DEGR cylinders, and may thus preventoverheating of the catalyst. As such, responsive to an indication thatdriver demanded engine torque equals or exceeds the engine output torquethreshold, default engine operating conditions may be resumed. Forexample, as described above, the engine may be operated at the torquelevel demand, with both non-DEGR cylinders and DEGR cylinders activated.

Turning now to FIG. 6, a flow chart for a high level example method 600for operating a hybrid vehicle engine in response to a tip-out event,where the engine comprises one or more dedicated EGR cylinders, isshown. More specifically, method 600 continues from method 400 and maybe used to rapidly shut down the engine responsive to a tip-out event,under circumstances where engine operation is not required andindependent of whether the charge state of the energy storage device isgreater than, or less than, the predetermined amount. In this way, thefast rising percent EGR that occurs during tip-out events and which mayresult in combustion instability may be avoided. Method 600 will bedescribed with reference to the systems described herein and shown inFIGS. 1-3, though it should be understood that similar methods may beapplied to other systems without departing from the scope of thisdisclosure. Method 600 may be carried out by a controller, such ascontroller 12 in FIG. 1, and may be stored at the controller asexecutable instructions in non-transitory memory. Instructions forcarrying out method 600 and the rest of the methods included herein maybe executed by the controller based on instructions stored on a memoryof the controller and in conjunction with signals received from sensorsof the engine system, such as the sensors described above with referenceto FIGS. 1-3. The controller may employ fuel system actuators such asfuel injectors (e.g., 66), spark plug (e.g., 92), etc., according to themethod below.

Method 600 begins at 602 and includes indicating whether engineoperation is required. As described above, engine operation may berequired if a vehicle operator has requested passenger heat, or airconditioning. If engine operation is required, method 600 may proceed tomethod 700 depicted in FIG. 7, and may include turning off the fuelinjector for the DEGR cylinder(s), as described in further detailtherein. Alternatively, if engine operation is not indicated to berequired at 602, method 600 may proceed to 604.

The rest of method 600 may proceed in similar fashion as described abovewith regard to steps 420-428 of method 400. To avoid redundancy, thesteps will be briefly reiterated here. However, it should be understoodthat each step proceeding from 604 in method 600 may comprise allaspects of method 400 with regard to steps 420-428. Further, it may beemphasized that responsive to a tip-out event, method 600 may proceeddirectly to disabling fuel to the engine as described in further detailbelow, without increasing engine torque above torque demand and charginga battery, even if battery SOC is lower than a threshold, as describedwith regard to method 400 illustrated in FIG. 4. By proceeding directlyto shutting down the engine, combustion stability issues resulting fromthe rapid percent increase in EGR that may occur during tip-out eventsmay be avoided.

Accordingly, at 604, method 600 includes disabling engine fueling, whichmay include stopping fuel injection to the engine cylinders, anddiscontinuing spark. Furthermore, the motor/generator of the hybridvehicle system may be operated such that the vehicle may be propelledusing motor torque. Proceeding to 606, purging of the remaining EGR inthe intake manifold may be expedited by spinning the engine unfueled viathe motor generator, with an intake throttle in the intake passage fullyopened. Spinning the engine unfueled may include operating themotor/generator using electrical energy from the system battery. In oneexample, the engine may be spun unfueled at an engine speed based on theengine speed before the fuel injectors were shut off. Another examplemay comprise the generator spinning the engine unfueled at a fraction ofthe engine speed that the engine was spinning immediately prior todisabling fuel injectors. Alternatively, the selected speed may be aspeed efficient for both the engine and the transmission. Other examplesmay include spinning the engine unfueled at a speed that is based on thevehicle speed, or based on a combination of vehicle speed and arotational speed of rotating components of the planetary geartransmission. Still other examples may include spinning the engineunfueled at an engine speed corresponding to a least cranking speed ofthe engine, to allow the engine to be rapidly restarted in the event ofa driver change-of-mind operation (e.g., a tip-out followed by a tip-inshortly thereafter). For example, as described above, responsive to anindication of an operator change of mind, the controller may start tofuel the engine and spin up the engine from the cranking speed so as tomeet operator torque demand. In still other examples, the engine may bespun unfueled at an engine speed that allows the EGR to be purged asfast as possible, and may be based on the intake EGR level at the timeof a tip-out event. Finally, instead of spinning continuously, theengine may be spun unfueled intermittently. In each of the abovedescribed examples, motor/generator setting may be adjusted to enablethe engine to be spun, at the selected engine speed. In someembodiments, each of the generator and the motor may be operated to spinthe engine at the selected speed, while in other embodiments, only thegenerator may need to be operated.

At 608, method 600 includes indicating whether the EGR has beensufficiently purged from the engine intake manifold. As described above,whether EGR has been sufficiently purged may include indicating whetherthe EGR in the intake is lower than a threshold, and may be based on anintake oxygen sensor (e.g., 24).

If the EGR is not lower than the threshold, then the controller maycontinue to spin the engine unfueled via the motor/generator until EGRis sufficiently purged. If EGR is lower than the threshold, then at 610,the routine includes spinning the engine to rest. For example, theengine may be spun to rest via the motor and thereafter the engine maybe maintained shutdown until engine restart conditions are met. In themeantime, the vehicle may continue to be propelled using motor torque.As such, this allows the EGR rate to be reset (for example, to zero)such that when the engine is restarted, combustion stability issues maynot be exacerbated by residual EGR in the engine intake.

Continuing to 612, as described above, restart conditions may be metresponsive to battery SOC below a threshold charge level, a heat or airconditioning request, torque demand greater than a threshold amount,etc. As described above, if during propelling the vehicle via motortorque, responsive to an indication that the charge state of the batteryexceeds a threshold charge level (e.g., predetermined value, or secondthreshold SOC), restart conditions may include ceasing the vehiclepropulsion from the battery (or other energy storage device), andresuming fueling the one or more cylinders that recirculate exhaust gasto the remaining cylinders while engine load may be quickly increasedabove the threshold torque demand by charging the system batteryaccording to the method depicted in FIG. 4, and further described inFIG. 5 and FIG. 8.

If engine restart conditions are not met, method 600 may includemaintaining the vehicle operational status, which may include continuingto propel the vehicle via motor torque, or if at some point a vehicleoff event is detected, maintaining the engine off during the vehicle offcondition until engine restart conditions are met.

If restart conditions are met at 612, method 600 may proceed to method500, depicted in FIG. 5, where it may be determined whether the enginerestart event comprises a hot start, or a cold start event, where engineoperation during the restart may be adjusted as described above.

Turning now to FIG. 7, a flow chart for a high level example method 700for operating a hybrid vehicle where the engine comprises one or moreDEGR cylinders, responsive to a tip-out event, or engine torque demandlower than a threshold, is shown. More specifically, method 700 maycontinue from method 400, or method 600, and may include turning off thefuel injector to the one or more DEGR cylinders responsive to a tip-outevent (FIG. 6), or an engine torque demand lower than the threshold anda battery SOC greater than a threshold (FIG. 4), under circumstanceswhere engine operation is required. In this way, if engine operation isrequired, for example due to a vehicle operator request for vehicle airconditioning or heat, engine operation may be maintained while fuelsupply to the one or more DEGR cylinders may be disabled, thusmitigating potential combustion instability issues associated withcontinued operation of the one or more DEGR cylinders. Method 700 willbe described with reference to the systems described herein and shown inFIGS. 1-3, though it should be understood that similar methods may beapplied to other systems without departing from the scope of thisdisclosure. Method 700 may be carried out by a controller, such ascontroller 12 in FIG. 1, and may be stored at the controller asexecutable instructions in non-transitory memory. Instructions forcarrying out method 700 and the rest of the methods included herein maybe executed by the controller based on instructions stored on a memoryof the controller and in conjunction with signals received from sensorsof the engine system, such as the sensors described above with referenceto FIGS. 1-3. The controller may employ fuel system actuators such asfuel injectors (e.g., 66), spark plug (e.g., 92), etc., according to themethod below.

Method 700 begins at 705 and includes stopping fuel supply to a DEGRcylinder(s). For example, the controller may signal a fuel injectoractuator to move to a desired position in order to stop fuel supply tothe DEGR cylinder. Accordingly, the fuel injector actuator may move tothe desired position, and fuel supply to the DEGR cylinder may bestopped. Furthermore, spark may be disabled to the DEGR cylinder. Withthe DEGR cylinder deactivated, the imbalance between the torque producedin cylinders carrying out combustion, and the torque of the deactivatedcylinders may result in increased engine vibration and harshness. Suchvibration and harshness may be experienced by the vehicle operator andthereby reduce vehicle drive feel. To reduce noise, vibration, andharshness (NVH), engine speed may be increased at 710 via themotor/generator, and at 715 the DEGR cylinder may be operated in theabsence of fuel. At 720, method 700 may include using the electric motorfor high-frequency cancellation of torque pulsations resulting from theimbalance between torque produced from combusting non-DEGR cylinders andtorque from non-combusting DEGR cylinders. For example, the motor may becontrolled to supply torque to the driveline of the vehicle to provide asubstantially similar level of torque as previous and/or subsequentfiring cylinders. By operating the DEGR cylinder after stopping fuel tothe DEGR cylinder, fresh air supplied to the intake through an intakethrottle may be pumped through the DEGR cylinder. The fresh air in theEGR system may displace EGR in the intake manifold. As such, EGR may bepurged from the intake system, resulting in a decrease in the EGR ratein the intake system and an increase in intake oxygen concentration. Inthis way, the remaining cylinders may be run at stoichiometry withoutEGR.

Proceeding to 725, method 700 may include indicating whether enginetorque demand is less than a threshold torque demand. For example, asdescribed above with regard to FIG. 4, the threshold torque demand maycomprise an engine load where a dedicated amount of EGR may result incombustion stability issues. If, at 725, engine torque demand is notlower than the threshold torque demand, method 700 may proceed to 730.At 730, method 700 may include indicating whether the EGR has beensufficiently purged from the engine intake manifold. For example, asdescribed above, it may be determined if EGR (flow, amount,concentration, level, etc.) in the intake is lower than a threshold,where the threshold may be based on EGR tolerance of the engine at lowengine load conditions. In one example, an intake oxygen sensor (e.g.,24) may be used to estimate EGR in the intake. If the EGR is not lowerthan the threshold, method 700 may continue to operate the engine fueledwith the DEGR cylinder deactivated to further purge the intake of EGR.If EGR is not lower than the threshold but engine torque demand isgreater than the threshold, then in addition to using the electric motorfor high frequency cancellation of torque pulsations due to theinactivation of the DEGR cylinder, additional torque may be provided viathe electric motor to propel the vehicle, in an assist-mode of vehicleoperation, as described above with regard to FIG. 4. Alternatively, ifEGR is lower than the threshold, method 700 may proceed to 735 and mayinclude resuming default engine operating conditions responsive to theincrease in engine torque demand above the threshold. For example,resuming default engine operating conditions may comprise activatingfueling to the deactivated DEGR cylinder, and resuming providing sparkto the DEGR cylinder. As the torque demand is greater than thethreshold, and EGR was sufficiently purged from the intake manifoldduring operating the engine fueled, by activating the DEGR cylinder at735 to resume default engine operating conditions, combustioninstability issues may be avoided.

Returning to 725, if it is indicated that engine torque demand remainsless than the threshold, method 700 may proceed to 740. At 740, method700 may include indicating whether engine operation is still required.In one example, engine operation may not still be required responsive toa vehicle operator discontinuing a request for engine heat or airconditioning. As such, at 740, if engine operation is still required andengine torque demand remains below the threshold, the engine may becontinued to operate fueled with the DEGR cylinder deactivated, and withthe electric motor providing high frequency cancellation of torquepulsations resulting from engine operation with the DEGR cylinderdeactivated. Alternatively, if engine operation is not indicated tostill be requested at 740, method 700 may proceed to 745. At 745, method700 may comprise indicating whether EGR has been sufficiently purgedfrom the engine intake manifold. As described above, in one example anintake oxygen sensor may be used to estimate EGR in the intake, and itmay be indicated whether EGR in the intake is lower than a threshold. Ifthe EGR in the intake is not lower than the threshold, the engine may becontinued to be operated fueled with the DEGR cylinder deactivated tosufficiently purge the intake of EGR. Alternatively, at 745, if it isindicated that EGR in the intake is below the threshold, method 700 mayproceed to 750 and may include stopping fuel injection to the non-DEGRengine cylinders, and discontinuing spark to the non-DEGR cylinders.Furthermore, at 750, method 700 may include operating themotor/generator of the hybrid vehicle system, such that the vehicle maybe propelled using motor torque instead of engine torque. By propellingthe vehicle by using motor torque, combustion instability issues may beavoided at torque demands below the threshold torque demand. Proceedingto 755, method 700 may include spinning the engine to rest. For example,the engine may be spun to rest via the motor and thereafter the enginemay be maintained shutdown until engine restart conditions are met. Inthe meantime, the vehicle may continue to be propelled using motortorque.

Proceeding to 760, as described above with regard to step 408 of method400, restart conditions may be met responsive to battery SOC below athreshold charge level, a heat or air conditioning request, torquedemand greater than a threshold amount, etc. As described above, ifduring propelling the vehicle via motor torque, responsive to anindication that the charge state of the battery exceeds a thresholdcharge level (e.g., predetermined value, or second threshold SOC),restart conditions may include ceasing the vehicle propulsion from thebattery (or other energy storage device), and resuming fueling the oneor more cylinders that recirculate exhaust gas to the remainingcylinders while engine load may be quickly increased above the thresholdtorque demand by charging the system battery according to the methoddepicted in FIG. 4, and further described in FIG. 5 and FIG. 8.

If engine restart conditions are not met, method 700 may includemaintaining the vehicle operational status, which may include continuingto propel the vehicle via motor torque, or if at some point a vehicleoff event is detected, maintaining the engine off during the vehicle offcondition until engine restart conditions are met.

If restart conditions are met at 760, method 700 may proceed to method500, depicted in FIG. 5 where it may be determined whether the enginerestart event comprises a hot start, or a cold start event, where engineoperation during the restart may be adjusted as described above.

FIG. 8 depicts an example timeline 800 for controlling hybrid vehicleoperation wherein one or more of the cylinders comprises a dedicated EGR(DEGR) cylinder using the methods described herein and with reference toFIGS. 4-7. Timeline 800 includes plot 805, indicating vehicle enginespeed, over time. Line 806 represents a threshold engine speed, abovewhich one or more DEGR cylinders may be activated during an engine hotstart event, or wherein an engine load may be increased via an electricmotor/generator by providing negative torque to the engine, such thatone or more DEGR cylinders may be activated during an engine cold startevent. Timeline 800 further includes plot 810, indicating engine torque,over time. Line 811 represents an engine output threshold torque level,below which engine operation with DEGR may result in combustionstability issues. Further, lines 812 and 813 indicate a vehicle operatordemanded torque, as compared to plot 810, which indicates actual enginetorque. Where a demanded engine torque is not specifically indicated, itmay be understood that demanded torque and actual torque are equal. Line814 represents an alternate example engine torque during a hot startevent, as described in further detail below. Timeline 800 furtherincludes plot 815, indicating a throttle position, over time. Timeline800 further includes plot 820, indicating a percent EGR in the intakemanifold of the vehicle engine, over time. Line 821 represents athreshold percent EGR, below which it may be indicated that EGR issufficiently purged from the intake manifold such that future enginerestarts may be initiated without residual EGR in the engine intake.Line 821 represents an alternate example percent EGR during a hot startevent, as described in further detail below. Timeline 800 furtherincludes plot 825, indicating motor/generator torque, over time. Forsimplicity, a negative motor/generator torque indicates the charging ofthe vehicle system battery, where a positive motor/generator torqueindicates torque that may be used to propel the vehicle via the vehicledrivetrain. Line 826 represents an alternate example motor/generatortorque during a hot start event, as described in further detail below.Timeline 800 further includes plot 830, indicating a vehicle batterystate of charge (SOC), over time. Line 831 represents a threshold SOCand may include a level of charge where the battery is not capable ofaccepting further charge. Line 832 represents a second threshold SOCwherein, during propelling a vehicle via motor torque responsive toengine torque demand below the engine output threshold torque level, ifthe SOC reaches the second threshold, the engine may be activated andengine load may be quickly increased above the threshold torque demandby charging the system battery according to the method depicted in FIG.4 Line 833 represents an alternative example battery SOC during a hotstart event, as described in further detail below. Timeline 800 furtherincludes plot 835, indicating the on or off state of non-DEGR cylindersin the vehicle over time, where the on state comprises a condition wherethe non-DEGR cylinders are supplied with fuel from one or more fuelinjectors, and spark is provided to initiate combustion. Timeline 800further includes plot 840, indicating whether fuel injection (and spark)is provided to one or more dedicated EGR cylinders, over time. Line 841represents an alternative example where fuel injection (and spark) areprovided to one or more dedicated EGR cylinders during a hot startevent, as described in further detail below. Timeline 800 furtherincludes plot 845, indicating a level of oxygen in the intake manifoldof the vehicle engine, over time. Line 846 represents a level of oxygenwhere it may be indicated that EGR is sufficiently purged from theintake manifold. Line 847 represents an alternative example of a levelof oxygen during a hot start event, as described in further detailbelow. Timeline 800 further includes plot 850, indicating whether arequest for vehicle cabin heat, or air conditioning, is requested, overtime. Timeline 800 further includes plot 855, indicating whether intakeand exhaust valves are activated on the one or more dedicated EGRcylinders, over time. For example, if valve activation is “off”, it maybe understood that the intake and exhaust valves are configured in aclosed conformation. Line 856 represents an alternative example wherethe intake and exhaust valves may be activated during a cold startevent. Line 857 represents an alternative example wherein the intake andexhaust valves may be activated responsive to a hot start event.

At time t₀, it may be understood that the vehicle is not in operation.In other words, time t₀ may represent a key-off event. Engine speed iszero (e.g., mph), indicated by plot 805, and the vehicle is not beingpropelled by battery power, indicated by plot 825. Accordingly, torqueis not provided via the engine, indicated by plot 810. As the engine isnot in operation, the percentage of EGR, indicated by plot 820, is belowa threshold, represented by line 821, indicating that EGR is purged fromthe engine intake. Accordingly, intake oxygen, as monitored by an intakeoxygen sensor (e.g., 24), is at a threshold level, represented by line846, where the threshold indicates a level of EGR below a definedpercent. Both non-DEGR, and DEGR cylinders are off, represented by plots835, and 840, respectively. Battery SOC, indicated by plot 830, is belowa threshold, represented by line 831, indicating that the battery mayaccept further charge. Throttle position is near a closed position,indicative of the throttle position at the vehicle off event, indicatedby plot 815. Furthermore, heat and/or air conditioning is not requested,indicated by plot 850.

At time t₁, a cold-start event is initiated. A cold-start event maycomprise an indication of an engine temperature (or engine coolanttemperature) below a threshold temperature (e.g. a catalyst light-offtemperature). Accordingly, non-DEGR cylinders may be operated byactuating the valves of the non-DEGR cylinders, and by supplying fueland spark to the non-DEGR cylinders for combustion. As such, enginespeed and torque increase. Further, at time t₁, fueling and spark to theDEGR cylinder(s) are maintained off. However, in some examples,indicated by line 856, the intake and exhaust valves may be activated onthe DEGR cylinder(s) in order to route air to the non-DEGR cylinderssuch that exhaust gases from the non-DEGR cylinders are lean ofstoichiometry. In such an example, ignition timing to the non-DEGRcylinders may additionally be retarded, to increase exhaust gas heat. Byactivating the DEGR intake and exhaust valves in the absence of fuelingthe DEGR cylinder(s), in addition to retarding ignition, an exhaustcatalyst may be more rapidly heated, as described above with regard toFIG. 5. As described above, in some examples, prior to activating theDEGR cylinder, the electric motor may be used for high frequencycancellation of torque pulsations resulting from the imbalance betweentorque produced from the combusting non-DEGR cylinders, and torque fromthe non-combusting DEGR cylinder. For example, the motor may becontrolled to supply torque to the driveline of the vehicle to provide asubstantially similar level of torque as previous and/or subsequentfiring cylinders. As such, noise, vibration, and harshness may bemitigated during engine startup events.

Between time t₁ and t₂, engine speed rises above the threshold level,and engine torque increases accordingly. By time t₂, engine speed isindicated to be stabilized above the threshold. However, engine torqueremains at a level where combustion stability issues may resultresponsive to operation of the engine with DEGR cylinder(s). In order torapidly enable the engine to operate with DEGR cylinders on, at time t₂,negative torque may be applied to the engine, indicated by plot 825, andfuel injection (and spark) to the DEGR cylinder(s) may be initiated. Insome examples, initiating fuel injection (and spark) to the DEGRcylinder(s) may comprise initiating fuel injection to the DEGR cylinderlast in the cylinder firing order, responsive to an indication that fuelinjection to the DEGR cylinder may be initiated. In other words,responsive to applying a negative torque to the engine to increaseactual engine torque, fuel injection to the DEGR cylinder may bescheduled such that the DEGR cylinder is activated last in the cylinderfiring order. By applying negative torque to the engine, the engine maybe operated with engine output torque at or above the engine outputtorque threshold represented by line 811, where the threshold mayrepresent a level of engine output torque where dedicated EGR does notresult in combustion stability issues. Accordingly, between time t₂ andt₃, actual engine output torque, represented by plot 810 is at theengine output threshold, whereas in the absence of the negative torqueapplied to the engine via the motor/generator, engine output torquewould remain below the engine output threshold, indicated by line 812.It may be understood that the duration comprising time t₂ to t₃, maycomprise a “warm-up” duration. In order to show sufficient detail of thewarm-up duration, the period between time t₂ and t₃ is shown asillustrated in FIG. 8, although it may be understood that the durationmay not be drawn to scale, and the warm-up duration may comprise ashorter, or longer period. As the DEGR cylinder is activated, thepercent EGR rises to a defined level, where the defined level maycomprise a percent EGR based on the ratio of non-DEGR cylinders to DEGRcylinders. For example, in a four cylinder engine, if one of thecylinders comprises a DEGR cylinder, then the EGR would be twenty-fivepercent in the intake manifold, if all cylinders are operated equally.Additionally, with negative torque applied to the engine, the systembattery SOC increases, as the engine output torque greater than demandedtorque is used to charge the system battery. In some examples, chargingthe system battery may include operating a vehicle generator, thegenerator coupled to the system battery. Furthermore, as DEGR isactivated at time t₂, between time t₂ and t₃, oxygen levels in theengine intake are indicated to decline, indicated by plot 845, as theoxygen is displaced by exhaust gas.

At time t₃, the vehicle begins accelerating. As such, throttle positionis indicated to open, as the gas pedal is depressed. Accordingly,demanded engine torque is indicated to increase, indicated by plot 812.However, between time t₃ and t₄, while demanded torque remains below theengine output threshold torque level, negative torque is maintainedapplied to the engine such that actual engine output torque remains atthe threshold and the excess torque is continued to be used to chargethe system battery.

At time t₄, demanded engine output torque reaches the engine outputtorque threshold level. Accordingly, negative torque to the engine isstopped, and the battery charging operation is similarly stopped.Between time t₄ and t₅, the throttle is further opened, as the gas pedalis depressed to a defined amount. As such, engine torque and enginespeed both are indicated to rise and plateau. Both non-DEGR cylindersand DEGR cylinder(s) remain activated, and both the percent EGR andoxygen level in engine intake remain stable.

At time t₅, throttle position is indicated to begin closing, a functionof the gas pedal being released slightly from its depressed state.Accordingly, between time t₅ and t₆, as the throttle closes, enginespeed and the level of engine torque demand declines. At time t₆, thelevel of engine output torque demand crosses the threshold, and as such,continued operation of the DEGR cylinder(s) may result in combustionstability issues. Thus, at time t₆, negative torque is applied to theengine via the motor, to maintain actual engine output torque above theengine output torque threshold level, although demanded torque asinferred by driver pedal, represented by line 813, continues to declinebelow the threshold. The amount of negative torque applied to the enginemay be just enough to raise the level of engine output torque to thethreshold level, in some examples, as depicted herein. In otherexamples, the amount of negative torque applied to the engine maycomprise a greater amount, and may in some cases be based on a level ofbattery charge. For example, responsive to a battery charge below athreshold, negative torque may be increased such that additionalcharging of the battery may be conducted. As such, between time t₆ andt₇, although demanded torque is below the engine output torquethreshold, by applying negative torque to the engine the actual engineoutput torque may be maintained at the threshold level, such that theDEGR cylinder(s) may be maintained activated without combustionstability issues. Accordingly, excess torque is continued to be used tocharge the system battery.

At time t₇, battery SOC reaches a level where the battery may not acceptfurther charge, represented by line 831. However, engine torque demandremains below the engine output torque threshold. As the battery SOC hasreached the threshold, engine torque may not be maintained at or abovethe engine output threshold level by continued charging of the systembattery. As such, it may be determined whether engine operation isrequired. As a request for heat or air conditioning is not indicated,represented by plot 850, engine operation is not indicated to berequired. If engine operation were required, fuel to the DEGR cylindermay be stopped, and the vehicle operated with combusting non-DEGRcylinders, where the motor may be controlled for high frequencycancellation of torque pulsations resulting from the imbalance betweentorque produced from the combusting non-DEGR cylinders, and torque fromthe non-combusting DEGR cylinder, as described in detail with regard tomethod 700. As engine operation is not indicated to be required, at timet₇, the engine is shut down, which includes deactivating fuel injectionand spark to both non-DEGR cylinders and DEGR cylinder(s). Furthermore,the motor may be activated to propel the vehicle via battery power, byproviding positive torque to the wheels via the vehicle drivetrain.

Between time t₇ and t₈, while the motor may be used to propel thevehicle, the motor/generator may additionally be used to spin the engineunfueled and without spark (both DEGR and non-DEGR cylinders), with theintake and exhaust valves maintained activated. As such, EGR may beturned into air, enabling the rapid purging of EGR from engine intake.Additionally, the intake throttle may be commanded open, indicated byplot 815. By opening the intake throttle fully during the spinning, thededicated EGR system and the air induction system may be purged ofexhaust residuals and replenished with fresh intake air. As such,between time t₇ and t₈, percent EGR is indicated to decline, whileintake oxygen is indicated to rise. As the motor is propelling thevehicle, and the engine is being spun unfueled, via battery power,between time t₇ and t₈ battery SOC decreases.

At time t₈, oxygen level in the engine intake is indicated to reach athreshold level represented by line 846, and as such, percent EGR in theengine intake may be indicated to similarly reach a threshold level,indicated by line 821. As such, it may be indicated at time t₈ that theengine intake is sufficiently purged of EGR. By purging the air intakeand EGR system of exhaust residuals, combustion stability issuesassociated with a subsequent restart of the engine may be reduced oravoided. With the intake and EGR system purged of exhaust residuals,spinning the engine unfueled may be discontinued. Accordingly, betweentime t₈ and t₉, the engine may be spun to rest, and the throttle may becommanded to a default position. The vehicle may be continued to bepropelled by the motor via battery power. As such, battery SOC maycontinue to decrease. However, as the battery SOC is not indicated toreach the second threshold SOC, represented by line 832, the vehicle iscontinued to be propelled via motor torque rather than activating theengine and quickly increasing engine load above the threshold torquedemand by charging the system battery to mitigate combustioninstability.

At time t₉, the vehicle is indicated to come to a stop, indicated bymotor torque stopping propelling the vehicle. In some examples, the stopmay indicate a refueling event. In other examples, the vehicle may bestopped at a traffic light, stop sign, etc. In this example, it mayadditionally be understood that the vehicle may comprise a start-stopsystem, where the vehicle engine may be restarted responsive to arequest for acceleration. For example, a request for acceleration mayinclude a vehicle operator releasing a brake pedal, or by initiatingdepressing of a gas pedal. Other examples for initiating an enginerestart responsive to a request for acceleration may include anyexamples commonly known in the art. As such, at time t₁₀, a hot-startevent may be initiated, as the engine was recently shut down and thus itmay be understood that engine temperature and/or engine coolanttemperature may remain above a threshold level.

Between time t₁₀ and t₁₃, two examples for controlling vehicle operationresponsive to a hot start event. One example is represented by solidlines, and an alternative second example is represented by dashed linesas described in further detail below. In the case where there is onlysolid lines, solid lines represent both examples. For simplicity of thedescription, the first example will initially be described in fulldetail, and subsequently the second example will be described.

In the first example, at time t₁₀, non-DEGR cylinders are activated,indicated by plot 835, and DEGR cylinder(s) remain off. Between time t₁₀and t₁₁, engine speed rises above the threshold level, and engine torqueincreases accordingly. By time t₁₁, engine speed is indicated to bestabilized above the threshold. As the engine startup event comprises ahot start event, a warm-up phase is not initiated. At time t₁₁, throttleposition is indicated to open, the result of the gas pedal beingdepressed. Engine speed and torque increase as the vehicle is propelledforward by the engine. During the period where non-DEGR cylinders arecombusting and DEGR cylinders are non-combusting, the motor/generatormay be used for high frequency cancellation of torque pulsationsresulting from the imbalance between torque produced from non-DEGRcylinders, and DEGR cylinder(s), as described above. At time t₁₂, enginetorque rises to the threshold level where dedicated EGR is not an issuefor combustion stability, and with engine speed above the thresholdlevel, fuel injection to the DEGR cylinder(s) is initiated. Accordingly,between time t₁₂ and t₁₃, percent EGR in the engine intake rises andstabilizes, while intake oxygen in the engine intake declines andsimilarly stabilizes. As the vehicle is propelled via the engine,battery SOC does not change, and no torque is provided by the motor.Engine speed and engine torque fluctuate based on driver demand, as afunction of throttle position.

Returning to time t₁₀, in an alternative second example, the non-DEGRcylinders may be activated, and the DEGR cylinder(s) may concurrently beactivated, indicated by dashed line 841. In a case where fueling (andspark) to the DEGR cylinder(s) commences at time t₁₀, the intake andexhaust valves on the DEGR cylinder may additionally be activated,indicated by dashed line 857. In such an alternate example, negativetorque may be applied to the engine, indicated by dashed line 826, toquickly increase actual engine torque to the engine output thresholdtorque, indicated by dashed line 814. Percent EGR begins to rise at timet₁₀, indicated by dashed line 821, the excess engine torque is appliedto the battery, indicated by dashed line 833, and oxygen in the intakemanifold begins to decline, indicated by dashed line 847.

Between time t₁₀ and t₁₂, percent EGR rises and stabilizes, oxygenlevels in the intake manifold decline and stabilize, and battery SOCincreases. At time t₁₂, engine torque demand reaches the threshold levelwhere dedicated EGR is not an issue for combustion stability, andaccordingly the engine may be operated at the torque level demand,without excess torque provided to charge the battery. Accordingly,between time t₁₂ and t₁₃, the vehicle is propelled via the engine,battery SOC does not change, and no torque is provided by the motor.Engine speed and engine torque fluctuate based on driver demand, as afunction of throttle position.

In this way, responsive to light engine loads where a key disadvantageof the use of dedicated EGR includes combustion stability issues, saidcombustion stability issues may be mitigated by the systems and methodsdescribed herein, thus enabling continued use of EGR under light engineloads. Furthermore, the use of a dedicated EGR cylinder as an “air pump”during cold start conditions, in conjunction with retarding ignition tothe non-dedicated EGR cylinders, may serve to rapidly increase thetemperature of an exhaust catalyst to a temperature sufficient toprocess exhaust emissions. As such, undesired emissions may be reducedunder cold start conditions, and the ability to continue to use EGRduring engine operation at light loads may reduce NOx emissions. Forexample, increasing vehicle engine power output and using excess torqueto charge an onboard energy storage device enables EGR to be maintainedfrom one or more dedicated EGR cylinders, while avoiding combustionstability issues and keeping NOx levels low.

The technical effect is to maintain engine operation at a level wherededicated EGR does not result in combustion stability issues, evenduring continued operation at light engine loads. Such an effect isrealized via combining the use of dedicated EGR cylinder(s) with avehicle capable of storing and using energy in an onboard energy storagedevice. Such a vehicle is not limited to a hybrid electric vehicle, butmay include any vehicle capable of capturing and utilizing energy in anonboard storage device. Some examples of energy storage devices otherthan batteries may include a mechanical flywheel storage device, or ahydraulic pressure accumulator. By combining the use of dedicated EGRwith a vehicle capable of storing and using energy in an onboard storagedevice, fuel economy benefits of the use of dedicated EGR may berealized using low cost hardware while reducing NOx emissions.

A further technical effect is to make use of a dedicated EGR cylinder asan air pump during cold start conditions. By activating the intake andexhaust valves of a dedicated EGR cylinder, while maintaining fuelingand spark shut off, air may be thus routed to the intake of the non-DEGRcylinders, resulting in exhaust gases lean of stoichiometry. Byadditionally retarding ignition on the non-DEGR cylinders under suchcold start conditions, the temperature of one or more exhaust catalystscoupled to the non-dedicated EGR cylinders may be rapidly heated, thuspotentially reducing undesired emissions during cold start conditions,without additional costs and complexity associated with additionalbypass lines, bypass valves, external oxygen sources, etc.

The systems described herein and with reference to FIGS. 1-3, along withthe methods described herein and with reference to FIGS. 4-7, may enableone or more systems and one or more methods. In one example, a methodcomprises coupling an exhaust from one or more cylinders of a multiplecylinder combustion engine to an intake manifold of the engine; andduring starting and warm-up of the engine under a first set of operatingconditions, shutting off fuel to the one or more cylinders whilemaintaining intake and exhaust valves activated on the one or morecylinders. In a first example of the method, the method further includeswherein the first set of operating conditions are related to temperatureof one or more exhaust catalysts being below a temperature needed forcatalytic activity. A second example of the method optionally includesthe first example and further includes wherein the temperature isdetermined from one or more of the following: a direct temperaturemeasurement of the one or more catalyst(s); temperature of a coolantcoupled to the engine; time since the engine was last running; adetermination of exhaust temperature based on engine running conditionssuch as load, speed, air/fuel ratio, and/or spark timing. A thirdexample of the method optionally includes any one or more or each of thefirst and second examples and further includes wherein starting andwarming up the engine under the first set of operating conditions byshutting off fuel to the one or more cylinders while maintaining intakeand exhaust valves activated on the one or more cylinders decreases alight-off time of the one or more exhaust catalysts, wherein light-offincludes the one or more catalysts being above the temperature neededfor catalytic activity. A fourth example of the method optionallyincludes any one or more or each of the first through third examples andfurther comprises retarding ignition of the engine during starting andwarm-up of the engine under the first set of operating conditions. Afifth example of the method optionally includes any one or more or eachof the first through fourth examples and further includes whereinoperating the one or more cylinders with intake and exhaust valvesactivated while fuel is shut off routes air instead of exhaust to theintake manifold of the engine, and the spark timing and fuel injectionto the remaining cylinders is adjusted to account for said air insteadof exhaust. A sixth example of the method optionally includes any one ormore or each of the first through fifth examples and further comprisessupplying fuel to the one or more cylinders and to remaining cylindersduring starting and of the engine under a second set of operatingconditions; where the remaining cylinders do not couple exhaust to theintake manifold of the engine. A seventh example of the methodoptionally includes any one or more or each of the first through sixthexamples and further includes wherein the second set of operatingconditions comprises one or more of the following: a determination thattemperature of one or more exhaust catalyst(s) is at or above apredetermined temperature; time since last engine start being less thana preselected time; an indication exhaust gas temperatures are above apredetermined value; or, temperature of a coolant coupled to the enginebeing above a threshold value. An eighth example of the methodoptionally includes any one or more or each of the first through seventhexamples and further includes wherein starting the engine under thesecond set of operating conditions further comprises: increasing enginetorque to at least an engine output torque threshold, the engine outputtorque threshold comprising a condition wherein coupling the exhaustfrom the one or more cylinders to the intake manifold of the engine doesnot result in combustion instability, and charging an onboard energystorage device when its energy storage capacity is indicated to be lessthan a predetermined amount; and wherein the onboard energy storagedevice comprises one or more of a battery, a mechanical flywheel storagedevice, or a hydraulic pressure accumulator. A ninth example of themethod optionally includes any one or more or each of the first througheighth examples and further comprises responsive to starting the engineunder the second set of operating conditions and wherein the energystorage capacity of the energy storage device is indicated to be greaterthan the predetermined amount; activating the engine by starting fuelinjection to the remaining cylinders, shutting off fuel to the one ormore cylinders and not activating intake and exhaust valves on the oneor more cylinders; monitoring an engine speed; and responsive to theengine speed reaching a threshold engine speed, where a rate of changein engine speed is further indicated to be less than a threshold rate ofchange: maintaining fuel injection to the remaining engine cylinders,and starting fuel injection to the one or more cylinders; where startingfuel injection to the one or more cylinders that couples exhaust to theintake manifold of the engine further comprises an indication of enginetorque demand greater than the engine output torque threshold.

Another example of a method comprises coupling an exhaust from one ormore cylinders of a multiple cylinder combustion engine to an intakemanifold of the engine; in a first condition, including a cold start andwarm-up of the engine when temperature of one or more exhaust catalystsis below a predetermined threshold temperature needed for catalyticactivity, shutting off fuel to the one or more cylinders whilemaintaining intake and exhaust valves activated on the one or morecylinders; and resuming fueling and maintaining activated intake andexhaust valves on the one or more cylinders in a second condition. In afirst example of the method, the method further includes wherein thesecond condition comprises an indication that temperature of one or moreexhaust catalysts has reached the predetermined threshold temperature. Asecond example of the method optionally includes the first example andfurther includes wherein the second condition is related to anindication of engine starting and warm-up. A third example of the methodoptionally includes any one or more or each of the first and secondexamples and further includes wherein the indication of engine startingcomprises an engine speed greater than a threshold speed, and a rate ofchange of engine speed less than a threshold change rate. A fourthexample of the method optionally includes any one or more or each of thefirst through third examples and further comprises in the secondcondition, responsive to an engine torque below an engine output torquethreshold, the engine output torque threshold comprising a conditionwherein coupling the exhaust from the one or more cylinders to theintake manifold of the engine does not result in combustion instability:increasing engine torque to at least the engine output torque threshold,and charging an onboard energy storage device; wherein an energy storagecapacity of the energy storage device is indicated to be less than apredetermined amount; wherein the onboard energy storage devicecomprises one or more of a battery, a mechanical flywheel storagedevice, or a hydraulic pressure accumulator; and wherein responsive toan indication that a desired engine torque is equal to or greater thanthe engine output torque threshold: maintaining activated the remainingengine cylinders and the one or more cylinders and operating the engineat the desired engine torque without charging the onboard storagedevice; where the remaining cylinders do not couple exhaust to theintake manifold of the engine. A fifth example of the method optionallyincludes any one or more or each of the first through fourth examplesand further comprises in the second condition, responsive to an enginetorque below an engine output torque threshold, and the energy storagecapacity of the energy storage device greater than the predeterminedamount: maintaining shutting off fuel to the one or more cylinders anddeactivating the intake and exhaust valves on the one or more cylinders,wherein deactivating the intake and exhaust valves comprises configuringboth the intake and exhaust valves closed; and responsive to anindication that the desired engine torque is equal to or greater thanthe engine output torque threshold: maintaining activated the remainingengine cylinders, and resuming fueling and activating intake and exhaustvalves on the one or more cylinders.

An example of a hybrid vehicle system comprises an engine including anintake passage and an exhaust passage; an energy storage device; vehiclewheels propelled using torque from one or more of the engine and energyfrom the energy storage device; a first set of one or more cylindersthat route engine exhaust to the exhaust passage, the first set ofcylinders comprising one or more intake valves and one or more exhaustvalves; a second set of one or more cylinders that route exhaustdirectly from the second set of cylinder(s) to an intake manifold of theengine, the second set of cylinders comprising one or more intake valvesand one or more exhaust valves; one or more emission control devicespositioned in the exhaust passage; and a controller, storinginstructions in non-transitory memory, that when executed, cause thecontroller to: in a first condition, shut off or maintain shut offfueling to the second set of cylinders, activate the intake and exhaustvalves on the second set of cylinders, and activate fueling and activatethe intake and exhaust valves on the first set of cylinders; in a secondcondition, maintain activated the intake and exhaust valves on thesecond set of cylinders and activate fueling to the second set ofcylinders; and control power output of the engine to a desired power topropel the vehicle driven by the engine at a desired speed, and whenengine loads are less than a preselected load and when a charge state ofthe energy storage device is less than a predetermined amount, increasethe power beyond the desired power, and charge the energy storage deviceto reduce the power to the desired power. In a first example, the systemfurther includes wherein the controller further stores instructions innon-transitory memory, that when executed, cause the controller to:indicate when engine loads are less than the preselected load and whencharge state of the energy storage device is greater than thepredetermined amount; stop fueling at least the second set of cylindersthat route exhaust gas to the intake manifold of the engine; and propelthe vehicle at least in part by energy from the energy storage device;wherein the onboard energy storage device comprises one or more of abattery, a mechanical flywheel storage device, or a hydraulic pressureaccumulator. A second example of the system optionally includes thefirst example and further includes wherein the controller further storesinstructions in non-transitory memory, that when executed, cause thecontroller to: indicate a temperature of the one or more emissioncontrol devices; wherein the first condition comprises temperature ofthe one or more emission control devices below a temperature needed forcatalytic activity; wherein the second condition comprises temperatureof the one or more emission control devices above the temperature neededfor catalytic activity; and wherein the temperature of the one or moreemission control devices is based on at least one of a directtemperature measurement of the one or more emission control devices, atemperature of a coolant coupled to the engine, a time since the enginewas last running, or a determination of exhaust temperature based onengine load, speed, air/fuel ratio, and/or spark timing. A third exampleof the system optionally includes any one or more or each of the firstand second examples and further includes wherein the controller furtherstores instructions in non-transitory memory, that when executed, causethe controller to: cease vehicle propulsion from the energy storagedevice and resume fueling the second set of cylinders responsive tocharge state of the energy storage device less than the predeterminedamount.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method, comprising: coupling an exhaustfrom one or more cylinders of a multiple cylinder combustion engine toan intake manifold of the engine; and during starting and warm-up of theengine under a first set of operating conditions, shutting off fuel andspark to the one or more cylinders while maintaining intake and exhaustvalves activated on the one or more cylinders.
 2. The method of claim 1,wherein the first set of operating conditions are related to temperatureof one or more exhaust catalysts being below a temperature needed forcatalytic activity.
 3. The method of claim 2, wherein the temperature isdetermined from one or more of the following: a direct temperaturemeasurement of the one or more catalyst(s); temperature of a coolantcoupled to the engine; time since the engine was last running; adetermination of exhaust temperature based on engine running conditionssuch as load, speed, air/fuel ratio, and/or spark timing.
 4. The methodof claim 2, wherein starting and warming up the engine under the firstset of operating conditions by shutting off fuel and spark to the one ormore cylinders while maintaining intake and exhaust valves activated onthe one or more cylinders decreases a light-off time of the one or moreexhaust catalysts, wherein light-off includes the one or more catalystsbeing above the temperature needed for catalytic activity.
 5. The methodof claim 1, further comprising retarding ignition of the engine duringstarting and warm-up of the engine under the first set of operatingconditions.
 6. The method of claim 1, wherein operating the one or morecylinders with intake and exhaust valves activated while fuel is shutoff routes air instead of exhaust to the intake manifold of the engine,and spark timing and fuel injection to the remaining cylinders isadjusted to account for said air instead of exhaust.
 7. The method ofclaim 1, further comprising supplying fuel and spark to the one or morecylinders and to remaining cylinders during starting and of the engineunder a second set of operating conditions; where the remainingcylinders do not couple exhaust to the intake manifold of the engine. 8.The method of claim 7, wherein the second set of operating conditionscomprises one or more of the following: a determination that temperatureof one or more exhaust catalyst(s) is at or above a predeterminedtemperature; time since last engine start being less than a preselectedtime; an indication exhaust gas temperatures are above a predeterminedvalue; or, temperature of a coolant coupled to the engine being above athreshold value.
 9. The method of claim 7, wherein starting the engineunder the second set of operating conditions further comprises:increasing engine torque to at least an engine output torque threshold,the engine output torque threshold comprising a condition whereincoupling the exhaust from the one or more cylinders to the intakemanifold of the engine does not result in combustion instability, andcharging an onboard energy storage device when its energy storagecapacity is indicated to be less than a predetermined amount; andwherein the onboard energy storage device comprises one or more of abattery, a mechanical flywheel storage device, or a hydraulic pressureaccumulator.
 10. The method of claim 9, further comprising: responsiveto starting the engine under the second set of operating conditions andwherein the energy storage capacity of the energy storage device isindicated to be greater than the predetermined amount; activating theengine by starting fuel injection and spark to the remaining cylinders,shutting off fuel and spark to the one or more cylinders and notactivating intake and exhaust valves on the one or more cylinders;monitoring an engine speed; and responsive to the engine speed reachinga threshold engine speed, where a rate of change in engine speed isfurther indicated to be less than a threshold rate of change:maintaining fuel injection to the remaining engine cylinders, andstarting fuel injection and spark to the one or more cylinders; wherestarting fuel injection and spark to the one or more cylinders thatcouples exhaust to the intake manifold of the engine further comprisesan indication of engine torque demand greater than the engine outputtorque threshold.
 11. A method, comprising: coupling an exhaust from oneor more cylinders of a multiple cylinder combustion engine to an intakemanifold of the engine; in a first condition, including a cold start andwarm-up of the engine when temperature of one or more exhaust catalystsis below a predetermined threshold temperature needed for catalyticactivity, shutting off fuel and spark to the one or more cylinders whilemaintaining intake and exhaust valves activated on the one or morecylinders; and resuming fueling and maintaining activated intake andexhaust valves on the one or more cylinders in a second condition. 12.The method of claim 11, wherein the second condition comprises anindication that temperature of one or more exhaust catalysts has reachedthe predetermined threshold temperature.
 13. The method of claim 11,wherein the second condition is related to an indication of enginestarting and warm-up.
 14. The method of claim 13, wherein the indicationof engine starting comprises an engine speed greater than a thresholdspeed, and a rate of change of engine speed less than a threshold changerate.
 15. The method of claim 11, further comprising: in the secondcondition, responsive to an engine torque below an engine output torquethreshold, the engine output torque threshold comprising a conditionwherein coupling the exhaust from the one or more cylinders to theintake manifold of the engine does not result in combustion instability:increasing engine torque to at least the engine output torque threshold,and charging an onboard energy storage device; wherein an energy storagecapacity of the energy storage device is indicated to be less than apredetermined amount; wherein the onboard energy storage devicecomprises one or more of a battery, a mechanical flywheel storagedevice, or a hydraulic pressure accumulator; and wherein responsive toan indication that a desired engine torque is equal to or greater thanthe engine output torque threshold: maintaining activated the remainingengine cylinders and the one or more cylinders and operating the engineat the desired engine torque without charging the onboard storagedevice; where the remaining cylinders do not couple exhaust to theintake manifold of the engine.
 16. The method of claim 15, furthercomprising: in the second condition, responsive to an engine torquebelow an engine output torque threshold, and the energy storage capacityof the energy storage device greater than the predetermined amount:maintaining shutting off fuel and spark to the one or more cylinders anddeactivating the intake and exhaust valves on the one or more cylinders,wherein deactivating the intake and exhaust valves comprises configuringboth the intake and exhaust valves closed; and responsive to anindication that the desired engine torque is equal to or greater thanthe engine output torque threshold: maintaining activated the remainingengine cylinders, and resuming fueling and spark, and activating intakeand exhaust valves on the one or more cylinders.
 17. A hybrid vehiclesystem, comprising: an engine including an intake passage and an exhaustpassage; an energy storage device; vehicle wheels propelled using torquefrom one or more of the engine and energy from the energy storagedevice; a first set of one or more cylinders that route engine exhaustto the exhaust passage, the first set of cylinders comprising one ormore intake valves and one or more exhaust valves; a second set of oneor more cylinders that route exhaust directly from the second set ofcylinder(s) to an intake manifold of the engine, the second set ofcylinders comprising one or more intake valves and one or more exhaustvalves; one or more emission control devices positioned in the exhaustpassage; and a controller, storing instructions in non-transitorymemory, that when executed, cause the controller to: in a firstcondition, shut off or maintain shut off fueling and spark to the secondset of cylinders, activate the intake and exhaust valves on the secondset of cylinders, and activate fueling and spark, and activate theintake and exhaust valves on the first set of cylinders; in a secondcondition, maintain activated the intake and exhaust valves on thesecond set of cylinders and activate fueling and spark to the second setof cylinders; and control power output of the engine to a desired powerto propel the vehicle driven by the engine at a desired speed, and whenengine loads are less than a preselected load and when a charge state ofthe energy storage device is less than a predetermined amount, increasethe power beyond the desired power, and charge the energy storage deviceto reduce the power to the desired power.
 18. The hybrid vehicle systemof claim 17, wherein the controller further stores instructions innon-transitory memory, that when executed, cause the controller to:indicate when engine loads are less than the preselected load and whencharge state of the energy storage device is greater than thepredetermined amount; stop fueling and spark to at least the second setof cylinders that route exhaust gas to the intake manifold of theengine; and propel the vehicle at least in part by energy from theenergy storage device; wherein the onboard energy storage devicecomprises one or more of a battery, a mechanical flywheel storagedevice, or a hydraulic pressure accumulator.
 19. The hybrid vehiclesystem of claim 17, wherein the controller further stores instructionsin non-transitory memory, that when executed, cause the controller to:indicate a temperature of the one or more emission control devices;wherein the first condition comprises temperature of the one or moreemission control devices below a temperature needed for catalyticactivity; wherein the second condition comprises temperature of the oneor more emission control devices above the temperature needed forcatalytic activity; and wherein the temperature of the one or moreemission control devices is based on at least one of a directtemperature measurement of the one or more emission control devices, atemperature of a coolant coupled to the engine, a time since the enginewas last running, or a determination of exhaust temperature based onengine load, speed, air/fuel ratio, and/or spark timing.
 20. The hybridvehicle system of claim 18, wherein the controller further storesinstructions in non-transitory memory, that when executed, cause thecontroller to: cease vehicle propulsion from the energy storage deviceand resume fueling and spark to the second set of cylinders responsiveto charge state of the energy storage device less than the predeterminedamount.